On Sun, Feb 11, 2024 at 5:09 PM Adam Ford <aford173@xxxxxxxxx> wrote:
>
> When using video sync pulses, the HFP, HBP, and HSA are divided between
> the available lanes if there is more than one lane. For certain
> timings and lane configurations, the HFP may not be evenly divisible.
> If the HFP is rounded down, it ends up being too small which can cause
> some monitors to not sync properly. In these instances, adjust htotal
> and hsync to round the HFP up, and recalculate the htotal.
>
Marek V and Marek S,
Would either of you be willing to test that this doesn't break your
applications?
thanks
adam
> Tested-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx> # Kontron BL i.MX8MM with HDMI monitor
> Signed-off-by: Adam Ford <aford173@xxxxxxxxx>
> ---
> V2: No changes
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index 8476650c477c..52939211fe93 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -1606,6 +1606,27 @@ static int samsung_dsim_atomic_check(struct drm_bridge *bridge,
> adjusted_mode->flags |= (DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC);
> }
>
> + /*
> + * When using video sync pulses, the HFP, HBP, and HSA are divided between
> + * the available lanes if there is more than one lane. For certain
> + * timings and lane configurations, the HFP may not be evenly divisible.
> + * If the HFP is rounded down, it ends up being too small which can cause
> + * some monitors to not sync properly. In these instances, adjust htotal
> + * and hsync to round the HFP up, and recalculate the htotal. Through trial
> + * and error, it appears that the HBP and HSA do not appearto need the same
> + * correction that HFP does.
> + */
> + if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE && dsi->lanes > 1) {
> + int hfp = adjusted_mode->hsync_start - adjusted_mode->hdisplay;
> + int remainder = hfp % dsi->lanes;
> +
> + if (remainder) {
> + adjusted_mode->hsync_start += remainder;
> + adjusted_mode->hsync_end += remainder;
> + adjusted_mode->htotal += remainder;
> + }
> + }
> +
> return 0;
> }
>
> --
> 2.43.0
>
