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pwm: rockchip: Round period/duty down on apply, up on get

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With CONFIG_PWM_DEBUG=y, the rockchip PWM driver produces warnings like
this:

  rockchip-pwm fd8b0010.pwm: .apply is supposed to round down
  duty_cycle (requested: 23529/50000, applied: 23542/50000)

This is because the driver chooses ROUND_CLOSEST for purported
idempotency reasons. However, it's possible to keep idempotency while
always rounding down in .apply().

Do this by making .get_state() always round up, and making .apply()
always round down. This is done with u64 maths, and setting both period
and duty to U32_MAX (the biggest the hardware can support) if they would
exceed their 32 bits confines.

Fixes: 12f9ce4a51 ("pwm: rockchip: Fix period and duty cycle approximation")
Fixes: 1ebb74cf35 ("pwm: rockchip: Add support for hardware readout")
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Link: https://lore.kernel.org/r/20250616-rockchip-pwm-rounding-fix-v2-1-a9c65acad7b6@collabora.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
This commit is contained in:
Nicolas Frattaroli 2025-06-16 17:14:17 +02:00 • committed by Uwe Kleine-König
parent fd0b06972a
commit 0b4d1abe5c
1 changed files with 20 additions and 13 deletions
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33
drivers/pwm/pwm-rockchip.c
View file

@ -8,6 +8,8 @@
#include <linux/clk.h> #include <linux/clk.h>
#include <linux/io.h> #include <linux/io.h>
#include <linux/limits.h>
#include <linux/math64.h>
#include <linux/module.h> #include <linux/module.h>
#include <linux/of.h> #include <linux/of.h>
#include <linux/platform_device.h> #include <linux/platform_device.h>
@ -61,6 +63,7 @@ static int rockchip_pwm_get_state(struct pwm_chip *chip,
struct pwm_state *state) struct pwm_state *state)
{ {
struct rockchip_pwm_chip *pc = to_rockchip_pwm_chip(chip); struct rockchip_pwm_chip *pc = to_rockchip_pwm_chip(chip);
u64 prescaled_ns = (u64)pc->data->prescaler * NSEC_PER_SEC;
u32 enable_conf = pc->data->enable_conf; u32 enable_conf = pc->data->enable_conf;
unsigned long clk_rate; unsigned long clk_rate;
u64 tmp; u64 tmp;
@ -78,12 +81,12 @@ static int rockchip_pwm_get_state(struct pwm_chip *chip,
clk_rate = clk_get_rate(pc->clk); clk_rate = clk_get_rate(pc->clk);
tmp = readl_relaxed(pc->base + pc->data->regs.period); tmp = readl_relaxed(pc->base + pc->data->regs.period);
tmp *= pc->data->prescaler * NSEC_PER_SEC; tmp *= prescaled_ns;
state->period = DIV_ROUND_CLOSEST_ULL(tmp, clk_rate); state->period = DIV_U64_ROUND_UP(tmp, clk_rate);
tmp = readl_relaxed(pc->base + pc->data->regs.duty); tmp = readl_relaxed(pc->base + pc->data->regs.duty);
tmp *= pc->data->prescaler * NSEC_PER_SEC; tmp *= prescaled_ns;
state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, clk_rate); state->duty_cycle = DIV_U64_ROUND_UP(tmp, clk_rate);
val = readl_relaxed(pc->base + pc->data->regs.ctrl); val = readl_relaxed(pc->base + pc->data->regs.ctrl);
state->enabled = (val & enable_conf) == enable_conf; state->enabled = (val & enable_conf) == enable_conf;
@ -103,8 +106,9 @@ static void rockchip_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
const struct pwm_state *state) const struct pwm_state *state)
{ {
struct rockchip_pwm_chip *pc = to_rockchip_pwm_chip(chip); struct rockchip_pwm_chip *pc = to_rockchip_pwm_chip(chip);
unsigned long period, duty; u64 prescaled_ns = (u64)pc->data->prescaler * NSEC_PER_SEC;
u64 clk_rate, div; u64 clk_rate, tmp;
u32 period_ticks, duty_ticks;
u32 ctrl; u32 ctrl;
clk_rate = clk_get_rate(pc->clk); clk_rate = clk_get_rate(pc->clk);
@ -114,12 +118,15 @@ static void rockchip_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
* bits, every possible input period can be obtained using the * bits, every possible input period can be obtained using the
* default prescaler value for all practical clock rate values. * default prescaler value for all practical clock rate values.
*/ */
div = clk_rate * state->period; tmp = mul_u64_u64_div_u64(clk_rate, state->period, prescaled_ns);
period = DIV_ROUND_CLOSEST_ULL(div, if (tmp > U32_MAX)
pc->data->prescaler * NSEC_PER_SEC); tmp = U32_MAX;
period_ticks = tmp;
div = clk_rate * state->duty_cycle; tmp = mul_u64_u64_div_u64(clk_rate, state->duty_cycle, prescaled_ns);
duty = DIV_ROUND_CLOSEST_ULL(div, pc->data->prescaler * NSEC_PER_SEC); if (tmp > U32_MAX)
tmp = U32_MAX;
duty_ticks = tmp;
/* /*
* Lock the period and duty of previous configuration, then * Lock the period and duty of previous configuration, then
@ -131,8 +138,8 @@ static void rockchip_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
writel_relaxed(ctrl, pc->base + pc->data->regs.ctrl); writel_relaxed(ctrl, pc->base + pc->data->regs.ctrl);
} }
writel(period, pc->base + pc->data->regs.period); writel(period_ticks, pc->base + pc->data->regs.period);
writel(duty, pc->base + pc->data->regs.duty); writel(duty_ticks, pc->base + pc->data->regs.duty);
if (pc->data->supports_polarity) { if (pc->data->supports_polarity) {
ctrl &= ~PWM_POLARITY_MASK; ctrl &= ~PWM_POLARITY_MASK;