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

Paul Kocialkowski
2019-02-12T15:30:51Z

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