Re: [PATCH 2/2] drm/mediatek: dpi/dsi: fix possible_crtcs calculation

[Nícolas F. R. A. Prado]

On Tue, Aug 29, 2023 at 03:19:41PM +0200, Michael Walle wrote:
> mtk_drm_find_possible_crtc_by_comp() assumed that the main path will
> always have the CRTC with id 0, the ext id 1 and the third id 2. This
> is only true if the paths are all available. But paths are optional (see
> also comment in mtk_drm_kms_init()), e.g. the main path might not be
> enabled or available at all. Then the CRTC IDs will shift one up, e.g.
> ext will be 1 and the third path will be 2.
> 
> To fix that, dynamically calculate the IDs by the precence of the paths.
> 
> Fixes: 5aa8e7647676 ("drm/mediatek: dpi/dsi: Change the getting possible_crtc way")
> Suggested-by: Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx>
> Signed-off-by: Michael Walle <mwalle@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c | 41 ++++++++++++++-------
>  1 file changed, 27 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> index 771f4e173353..f3064bff64e8 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
> @@ -526,21 +526,34 @@ unsigned int mtk_drm_find_possible_crtc_by_comp(struct drm_device *drm,
>  						struct device *dev)
>  {
>  	struct mtk_drm_private *private = drm->dev_private;
> -	unsigned int ret = 0;
> -
> -	if (mtk_drm_find_comp_in_ddp(dev, private->data->main_path, private->data->main_len,
> -				     private->ddp_comp))
> -		ret = BIT(0);
> -	else if (mtk_drm_find_comp_in_ddp(dev, private->data->ext_path,
> -					  private->data->ext_len, private->ddp_comp))
> -		ret = BIT(1);
> -	else if (mtk_drm_find_comp_in_ddp(dev, private->data->third_path,
> -					  private->data->third_len, private->ddp_comp))
> -		ret = BIT(2);
> -	else
> -		DRM_INFO("Failed to find comp in ddp table\n");
> +	int i = 0;
> +
> +	if (private->data->main_path) {
> +		if (mtk_drm_find_comp_in_ddp(dev, private->data->main_path,
> +					     private->data->main_len,
> +					     private->ddp_comp))
> +			return BIT(i);
> +		i++;
> +	}
> +
> +	if (private->data->ext_path) {
> +		if (mtk_drm_find_comp_in_ddp(dev, private->data->ext_path,
> +					     private->data->ext_len,
> +					     private->ddp_comp))
> +			return BIT(i);
> +		i++;

This won't work. On MT8195 there are two display IPs, vdosys0 and vdosys1,
vdosys0 only has the main path while vdosys1 only has the external path. So you
need to loop over each one in all_drm_private[j] to get the right crtc ID for
MT8195.

Thanks,
Nícolas