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Andy Chiu b690f8df64 net: axienet: Use iowrite64 to write all 64b descriptor pointers 
According to commit f735c40ed9 ("net: axienet: Autodetect 64-bit DMA
capability") and AXI-DMA spec (pg021), on 64-bit capable dma, only
writing MSB part of tail descriptor pointer causes DMA engine to start
fetching descriptors. However, we found that it is true only if dma is in
idle state. In other words, dma would use a tailp even if it only has LSB
updated, when the dma is running.

The non-atomicity of this behavior could be problematic if enough
delay were introduced in between the 2 writes. For example, if an
interrupt comes right after the LSB write and the cpu spends long
enough time in the handler for the dma to get back into idle state by
completing descriptors, then the seconcd write to MSB would treat dma
to start fetching descriptors again. Since the descriptor next to the
one pointed by current tail pointer is not filled by the kernel yet,
fetching a null descriptor here causes a dma internal error and halt
the dma engine down.

We suggest that the dma engine should start process a 64-bit MMIO write
to the descriptor pointer only if ONE 32-bit part of it is written on all
states. Or we should restrict the use of 64-bit addressable dma on 32-bit
platforms, since those devices have no instruction to guarantee the write
to LSB and MSB part of tail pointer occurs atomically to the dma.

initial condition:
curp =  x-3;
tailp = x-2;
LSB = x;
MSB = 0;

cpu:                       |dma:
 iowrite32(LSB, tailp)     |  completes #(x-3) desc, curp = x-3
 ...                       |  tailp updated
 => irq                    |  completes #(x-2) desc, curp = x-2
    ...                    |  completes #(x-1) desc, curp = x-1
    ...                    |  ...
    ...                    |  completes #x desc, curp = tailp = x
 <= irqreturn              |  reaches tailp == curp = x, idle
 iowrite32(MSB, tailp + 4) |  ...
                           |  tailp updated, starts fetching...
                           |  fetches #(x + 1) desc, sees cntrl = 0
                           |  post Tx error, halt

Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Reported-by: Max Hsu <max.hsu@sifive.com>
Reviewed-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2022-06-13 12:36:55 +01:00
arch arm64 fixes for 5.19-rc2: 2022-06-10 11:03:51 -07:00
block for-5.19/drivers-2022-06-02 2022-06-03 10:25:56 -07:00
certs certs: Convert spaces in certs/Makefile to a tab 2022-06-10 11:42:02 -07:00
crypto This update includes the following changes: 2022-05-27 18:06:49 -07:00
Documentation Documentation: add description for net.sctp.ecn_enable 2022-06-10 22:18:20 -07:00
drivers net: axienet: Use iowrite64 to write all 64b descriptor pointers 2022-06-13 12:36:55 +01:00
fs zonefs fixes for 5.19-rc2 2022-06-10 10:56:28 -07:00
include ATA fixes for 5.19-rc2 2022-06-10 10:30:43 -07:00
init gcc-12: disable '-Warray-bounds' universally for now 2022-06-09 10:11:12 -07:00
ipc These changes update the ipc sysctls so that they are fundamentally 2022-06-03 15:54:57 -07:00
kernel Power management fixes for 5.19-rc2 2022-06-10 11:49:27 -07:00
lib Bitmap patches for 5.19-rc1 2022-06-04 14:04:27 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm Hot fixes for 5.19-rc1. 2022-06-05 17:05:38 -07:00
net net: seg6: fix seg6_lookup_any_nexthop() to handle VRFs using flowi_l3mdev 2022-06-09 22:04:47 -07:00
samples drm for 5.19-rc1 2022-05-25 16:18:27 -07:00
scripts cert host tools: Stop complaining about deprecated OpenSSL functions 2022-06-08 13:18:39 -07:00
security KEYS: trusted: tpm2: Fix migratable logic 2022-06-08 14:12:13 +03:00
sound sound fixes for 5.19-rc2 2022-06-10 10:20:57 -07:00
tools Networking fixes for 5.19-rc2, including fixes from bpf and netfilter. 2022-06-09 12:06:52 -07:00
usr Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
virt * Fix syzkaller NULL pointer dereference 2022-06-08 09:16:31 -07:00
.clang-format clang-format: Fix space after for_each macros 2022-05-20 19:27:16 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore kbuild: split the second line of *.mod into *.usyms 2022-05-08 03:16:59 +09:00
.mailmap Hot fixes for 5.19-rc1. 2022-06-05 17:05:38 -07:00
COPYING
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
Kbuild
Kconfig
MAINTAINERS Devicetree fixes for 5.19, part 2: 2022-06-10 11:57:36 -07:00
Makefile gcc-12: disable '-Warray-bounds' universally for now 2022-06-09 10:11:12 -07:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.