From: Thierry Reding treding@nvidia.com
[ Upstream commit 95dcd64bc5a27080beaa344edfe5bdcca3d2e7dc ]
Technically this is not required because disabling the PWM should be enough. However, when support for atomic operations was implemented in the PWM subsystem, only actual changes to the PWM channel are applied during pwm_config(), which means that during after resume from suspend the old settings won't be applied.
One possible solution is for the PWM driver to implement its own PM operations such that settings from before suspend get applied on resume. This has the disadvantage of completely ignoring any particular ordering requirements that PWM user drivers might have, so it is best to leave it up to the user drivers to apply the settings that they want at the appropriate time.
Another way to solve this would be to read back the current state of the PWM at the time of resume. That way, in case the configuration was lost during suspend, applying the old settings in PWM user drivers would actually get them applied because they differ from the current settings. However, not all PWM drivers support reading the hardware state, and not all hardware may support it.
The best workaround at this point seems to be to let PWM user drivers tell the PWM subsystem that the PWM is turned off by, in addition to disabling it, also setting the duty cycle to 0. This causes the resume operation to apply a configuration that is different from the current configuration, resulting in the proper state from before suspend getting restored.
Signed-off-by: Thierry Reding treding@nvidia.com Signed-off-by: Guenter Roeck linux@roeck-us.net Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/hwmon/pwm-fan.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c index 7838af58f92d..9d611dd268e1 100644 --- a/drivers/hwmon/pwm-fan.c +++ b/drivers/hwmon/pwm-fan.c @@ -290,9 +290,19 @@ static int pwm_fan_remove(struct platform_device *pdev) static int pwm_fan_suspend(struct device *dev) { struct pwm_fan_ctx *ctx = dev_get_drvdata(dev); + struct pwm_args args; + int ret; + + pwm_get_args(ctx->pwm, &args); + + if (ctx->pwm_value) { + ret = pwm_config(ctx->pwm, 0, args.period); + if (ret < 0) + return ret;
- if (ctx->pwm_value) pwm_disable(ctx->pwm); + } + return 0; }