Re: [PATCH] Revert "pwm: Let pwm_get_state() return the last implemented state"

[Enric Balletbo i Serra <enric.balletbo@collabora.com>]

On 21/10/19 12:58, Thierry Reding wrote:
> It turns out that commit 01ccf903edd6 ("pwm: Let pwm_get_state() return
> the last implemented state") causes backlight failures on a number of
> boards. The reason is that some of the drivers do not write the full
> state through to the hardware registers, which means that ->get_state()
> subsequently does not return the correct state. Consumers which rely on
> pwm_get_state() returning the current state will therefore get confused
> and subsequently try to program a bad state.
> 
> Before this change can be made, existing drivers need to be more
> carefully audited and fixed to behave as the framework expects. Until
> then, keep the original behaviour of returning the software state that
> was applied rather than reading the state back from hardware.
> 
> Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

Thanks,
 Enric.

> ---
>  drivers/pwm/core.c | 9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 6ad51aa60c03..f877e77d9184 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -472,14 +472,7 @@ int pwm_apply_state(struct pwm_device *pwm, const struct pwm_state *state)
>  		if (err)
>  			return err;
>  
> -		/*
> -		 * .apply might have to round some values in *state, if possible
> -		 * read the actually implemented value back.
> -		 */
> -		if (chip->ops->get_state)
> -			chip->ops->get_state(chip, pwm, &pwm->state);
> -		else
> -			pwm->state = *state;
> +		pwm->state = *state;
>  	} else {
>  		/*
>  		 * FIXME: restore the initial state in case of error.
>