[PATCH 2/4] drm/sun4i: dsi: Change the start delay calculation

[Paul Kocialkowski]

Hi,

On Wed, 2019-01-23 at 16:54 +0100, Maxime Ripard wrote:
> The current calculation for the video start delay in the current DSI driver
> is that it is the total vertical size, minus the backporch and sync length,
> plus 1.
> 
> However, the Allwinner code has it as the active vertical size, plus the
> back porch and the sync length. This doesn't make any difference on the
> only panel it has been tested with so far, since in that particular case
> the front porch is equal to the sum of the back porch and sync length.
> 
> This is not the case for all panels, obviously, so we need to fix it. Since
> the Allwinner code has a bunch of extra code to deal with out of bounds
> values, so let's add them as well.
> 
> Signed-off-by: Maxime Ripard <maxime.ripard at bootlin.com>
> ---
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> index 380fc527a707..e3e4ba90c059 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -357,7 +357,12 @@ static void sun6i_dsi_inst_init(struct sun6i_dsi *dsi,
>  static u16 sun6i_dsi_get_video_start_delay(struct sun6i_dsi *dsi,
>  					   struct drm_display_mode *mode)
>  {
> -	return mode->vtotal - (mode->vsync_end - mode->vdisplay) + 1;
> +	u16 delay = (mode->vsync_end + 1) % mode->vtotal;
> +
> +	if (!delay)
> +		delay = 1;

For increased clarity, you might want to change this last block to:

delay = max(delay, 1);

Cheers,

Paul

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