Re: [PATCH v3 3/8] drm/sun4i: dsi: Enforce boundaries on the start delay

[Paul Kocialkowski <paul.kocialkowski@bootlin.com>]

Hi,

On Mon, 2019-02-11 at 15:41 +0100, Maxime Ripard wrote:
> The Allwinner BSP makes sure that we don't end up with a null start delay
> or with a delay larger than vtotal.
> 
> The former condition is likely to happen now with the reworked start delay,
> so make sure we enforce the same boundaries.
> 
> Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>

Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>

> ---
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> index 9471fa695ec7..506f2e8cf454 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -358,8 +358,12 @@ static u16 sun6i_dsi_get_video_start_delay(struct sun6i_dsi *dsi,
>  					   struct drm_display_mode *mode)
>  {
>  	u16 start = clamp(mode->vtotal - mode->vdisplay - 10, 8, 100);
> +	u16 delay = mode->vtotal - (mode->vsync_end - mode->vdisplay) + start;
>  
> -	return mode->vtotal - (mode->vsync_end - mode->vdisplay) + start;
> +	if (delay > mode->vtotal)
> +		delay = delay % mode->vtotal;

I wonder whether delay == mode->vtotal would make sense at all. If not,
then we can just apply the modulo unconditionally. But in doubt, let's
keep things this way.

Cheers,

Paul

> +
> +	return max_t(u16, delay, 1);
>  }
>  
>  static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com


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