linux/arch/mips/include/asm/timex.h

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/*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Copyright (C) 1998, 1999, 2003 by Ralf Baechle
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
* Copyright (C) 2014 by Maciej W. Rozycki
*/
#ifndef _ASM_TIMEX_H
#define _ASM_TIMEX_H
#ifdef __KERNEL__
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
#include <linux/compiler.h>
#include <asm/cpu.h>
#include <asm/cpu-features.h>
#include <asm/mipsregs.h>
#include <asm/cpu-type.h>
/*
* This is the clock rate of the i8253 PIT. A MIPS system may not have
* a PIT by the symbol is used all over the kernel including some APIs.
* So keeping it defined to the number for the PIT is the only sane thing
* for now.
*/
#define CLOCK_TICK_RATE 1193182
/*
* Standard way to access the cycle counter.
* Currently only used on SMP for scheduling.
*
* Only the low 32 bits are available as a continuously counting entity.
* But this only means we'll force a reschedule every 8 seconds or so,
* which isn't an evil thing.
*
* We know that all SMP capable CPUs have cycle counters.
*/
typedef unsigned int cycles_t;
/*
MIPS: Fix CP0 counter erratum detection for R4k CPUs Fix the discrepancy between the two places we check for the CP0 counter erratum in along with the incorrect comparison of the R4400 revision number against 0x30 which matches none and consistently consider all R4000 and R4400 processors affected, as documented in processor errata publications[1][2][3], following the mapping between CP0 PRId register values and processor models: PRId | Processor Model ---------+-------------------- 00000422 | R4000 Revision 2.2 00000430 | R4000 Revision 3.0 00000440 | R4400 Revision 1.0 00000450 | R4400 Revision 2.0 00000460 | R4400 Revision 3.0 No other revision of either processor has ever been spotted. Contrary to what has been stated in commit ce202cbb9e0b ("[MIPS] Assume R4000/R4400 newer than 3.0 don't have the mfc0 count bug") marking the CP0 counter as buggy does not preclude it from being used as either a clock event or a clock source device. It just cannot be used as both at a time, because in that case clock event interrupts will be occasionally lost, and the use as a clock event device takes precedence. Compare against 0x4ff in `can_use_mips_counter' so that a single machine instruction is produced. References: [1] "MIPS R4000PC/SC Errata, Processor Revision 2.2 and 3.0", MIPS Technologies Inc., May 10, 1994, Erratum 53, p.13 [2] "MIPS R4400PC/SC Errata, Processor Revision 1.0", MIPS Technologies Inc., February 9, 1994, Erratum 21, p.4 [3] "MIPS R4400PC/SC Errata, Processor Revision 2.0 & 3.0", MIPS Technologies Inc., January 24, 1995, Erratum 14, p.3 Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> Fixes: ce202cbb9e0b ("[MIPS] Assume R4000/R4400 newer than 3.0 don't have the mfc0 count bug") Cc: stable@vger.kernel.org # v2.6.24+ Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
2022-04-24 12:46:23 +01:00
* On R4000/R4400 an erratum exists such that if the cycle counter is
* read in the exact moment that it is matching the compare register,
* no interrupt will be generated.
*
* There is a suggested workaround and also the erratum can't strike if
* the compare interrupt isn't being used as the clock source device.
* However for now the implementation of this function doesn't get these
* fine details right.
*/
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
static inline int can_use_mips_counter(unsigned int prid)
{
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
int comp = (prid & PRID_COMP_MASK) != PRID_COMP_LEGACY;
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
if (__builtin_constant_p(cpu_has_counter) && !cpu_has_counter)
return 0;
else if (__builtin_constant_p(cpu_has_mips_r) && cpu_has_mips_r)
return 1;
else if (likely(!__builtin_constant_p(cpu_has_mips_r) && comp))
return 1;
/* Make sure we don't peek at cpu_data[0].options in the fast path! */
if (!__builtin_constant_p(cpu_has_counter))
asm volatile("" : "=m" (cpu_data[0].options));
if (likely(cpu_has_counter &&
MIPS: Fix CP0 counter erratum detection for R4k CPUs Fix the discrepancy between the two places we check for the CP0 counter erratum in along with the incorrect comparison of the R4400 revision number against 0x30 which matches none and consistently consider all R4000 and R4400 processors affected, as documented in processor errata publications[1][2][3], following the mapping between CP0 PRId register values and processor models: PRId | Processor Model ---------+-------------------- 00000422 | R4000 Revision 2.2 00000430 | R4000 Revision 3.0 00000440 | R4400 Revision 1.0 00000450 | R4400 Revision 2.0 00000460 | R4400 Revision 3.0 No other revision of either processor has ever been spotted. Contrary to what has been stated in commit ce202cbb9e0b ("[MIPS] Assume R4000/R4400 newer than 3.0 don't have the mfc0 count bug") marking the CP0 counter as buggy does not preclude it from being used as either a clock event or a clock source device. It just cannot be used as both at a time, because in that case clock event interrupts will be occasionally lost, and the use as a clock event device takes precedence. Compare against 0x4ff in `can_use_mips_counter' so that a single machine instruction is produced. References: [1] "MIPS R4000PC/SC Errata, Processor Revision 2.2 and 3.0", MIPS Technologies Inc., May 10, 1994, Erratum 53, p.13 [2] "MIPS R4400PC/SC Errata, Processor Revision 1.0", MIPS Technologies Inc., February 9, 1994, Erratum 21, p.4 [3] "MIPS R4400PC/SC Errata, Processor Revision 2.0 & 3.0", MIPS Technologies Inc., January 24, 1995, Erratum 14, p.3 Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> Fixes: ce202cbb9e0b ("[MIPS] Assume R4000/R4400 newer than 3.0 don't have the mfc0 count bug") Cc: stable@vger.kernel.org # v2.6.24+ Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
2022-04-24 12:46:23 +01:00
prid > (PRID_IMP_R4000 | PRID_REV_ENCODE_44(15, 15))))
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
return 1;
else
return 0;
}
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
static inline cycles_t get_cycles(void)
{
if (can_use_mips_counter(read_c0_prid()))
return read_c0_count();
else
return 0; /* no usable counter */
}
#define get_cycles get_cycles
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
/*
* Like get_cycles - but where c0_count is not available we desperately
* use c0_random in an attempt to get at least a little bit of entropy.
*/
static inline unsigned long random_get_entropy(void)
{
unsigned int c0_random;
if (can_use_mips_counter(read_c0_prid()))
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
return read_c0_count();
if (cpu_has_3kex)
c0_random = (read_c0_random() >> 8) & 0x3f;
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
else
c0_random = read_c0_random() & 0x3f;
return (random_get_entropy_fallback() << 6) | (0x3f - c0_random);
}
MIPS: Implement random_get_entropy with CP0 Random Update to commit 9c9b415c50bc298ac61412dff856eae2f54889ee [MIPS: Reimplement get_cycles().] On systems were for whatever reasons we can't use the cycle counter, fall back to the c0_random register as an entropy source. It has however a very small range that makes it suitable for random_get_entropy only and not get_cycles. This optimised version compiles to 8 instructions in the fast path even in the worst case of all the conditions to check being variable (including a MFC0 move delay slot that is only required for very old processors): 828: 8cf90000 lw t9,0(a3) 828: R_MIPS_LO16 jiffies 82c: 40057800 mfc0 a1,c0_prid 830: 3c0200ff lui v0,0xff 834: 00a21024 and v0,a1,v0 838: 1040007d beqz v0,a30 <add_interrupt_randomness+0x22c> 83c: 3c030000 lui v1,0x0 83c: R_MIPS_HI16 cpu_data 840: 40024800 mfc0 v0,c0_count 844: 00000000 nop 848: 00409021 move s2,v0 84c: 8ce20000 lw v0,0(a3) 84c: R_MIPS_LO16 jiffies On most targets the sequence will be shorter and on some it will reduce to a single `MFC0 <reg>,c0_count', as all MIPS architecture (i.e. non-legacy MIPS) processors require the CP0 Count register to be present. The only known exception that reports MIPS architecture compliance, but contrary to that lacks CP0 Count is the Ingenic JZ4740 thingy. For broken platforms like that this code requires cpu_has_counter to be hardcoded to 0 (i.e. no variable setting is permitted) so as not to penalise all the other good platforms out there. The asm barrier is required so that the compiler does not pull any potentially costly (cold cache!) `cpu_data' variable access into the fast path. Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Cc: Theodore Ts'o <tytso@mit.edu> Cc: John Crispin <blogic@openwrt.org> Cc: Andrew McGregor <andrewmcgr@gmail.com> Cc: Dave Taht <dave.taht@bufferbloat.net> Cc: Felix Fietkau <nbd@nbd.name> Cc: Simon Kelley <simon@thekelleys.org.uk> Cc: Jim Gettys <jg@freedesktop.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/6702/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-04-06 21:31:29 +01:00
#define random_get_entropy random_get_entropy
#endif /* __KERNEL__ */
#endif /* _ASM_TIMEX_H */