[PATCH] pwm: rockchip: Keep enabled PWMs running while probing

[Heiko Stübner]

Hi Simon,

Am Freitag, 18. September 2020, 22:48:25 CEST schrieb Simon South:
> Following commit cfc4c189bc70 ("pwm: Read initial hardware state at
> request time") the Rockchip PWM driver can no longer assume a device's
> pwm_state structure has been populated after a call to pwmchip_add().
> Consequently, the test in rockchip_pwm_probe() intended to prevent the
> driver from stopping PWM devices already enabled by the bootloader no
> longer functions reliably and this can lead to the kernel hanging
> during startup, particularly on devices like the Pinebook Pro that use
> a PWM-controlled backlight for their display.
> 
> Avoid this by querying the device directly at probe time to determine
> whether or not it is enabled.
> 
> Signed-off-by: Simon South <simon at simonsouth.net>

On first glance this looks like a good catch but there is a bit of
housekeeping missing.

The patch should get a fixes tag like
Fixes: cfc4c189bc70 ("pwm: Read initial hardware state at request time")

Can you resend the patch and include relevant other parties like you get
from  'scripts/get_maintainer.pl -f drivers/pwm/pwm-rockchip.c' like

Thierry Reding <thierry.reding at gmail.com> (maintainer:PWM SUBSYSTEM)
"Uwe Kleine-König" <u.kleine-koenig at pengutronix.de> (reviewer:PWM SUBSYSTEM)
Lee Jones <lee.jones at linaro.org> (maintainer:PWM SUBSYSTEM)
linux-pwm at vger.kernel.org (open list:PWM SUBSYSTEM)


Thanks
Heiko

> ---
>  drivers/pwm/pwm-rockchip.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-rockchip.c b/drivers/pwm/pwm-rockchip.c
> index eb8c9cb645a6..098e94335cb5 100644
> --- a/drivers/pwm/pwm-rockchip.c
> +++ b/drivers/pwm/pwm-rockchip.c
> @@ -288,6 +288,7 @@ static int rockchip_pwm_probe(struct platform_device *pdev)
>  	const struct of_device_id *id;
>  	struct rockchip_pwm_chip *pc;
>  	struct resource *r;
> +	u32 enable_conf, ctrl;
>  	int ret, count;
>  
>  	id = of_match_device(rockchip_pwm_dt_ids, &pdev->dev);
> @@ -362,7 +363,9 @@ static int rockchip_pwm_probe(struct platform_device *pdev)
>  	}
>  
>  	/* Keep the PWM clk enabled if the PWM appears to be up and running. */
> -	if (!pwm_is_enabled(pc->chip.pwms))
> +	enable_conf = pc->data->enable_conf;
> +	ctrl = readl_relaxed(pc->base + pc->data->regs.ctrl);
> +	if ((ctrl & enable_conf) != enable_conf)
>  		clk_disable(pc->clk);
>  
>  	return 0;
>