Quoting Abhinav Kumar (2024-07-30 10:55:40)
> Fix the dp_panel_get_supported_bpp() API to return the minimum
> supported bpp correctly for relevant cases and use this API
> to correct the behavior of DP driver which hard-codes the max supported
> bpp to 30.
>
> This is incorrect because the number of lanes and max data rate
> supported by the lanes need to be taken into account.
>
> Replace the hardcoded limit with the appropriate math which accounts
> for the accurate number of lanes and max data rate.
>
> changes in v2:
> - Fix the dp_panel_get_supported_bpp() and use it
> - Drop the max_t usage as dp_panel_get_supported_bpp() already
> returns the min_bpp correctly now
>
> Fixes: c943b4948b58 ("drm/msm/dp: add displayPort driver support")
> Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/43
> Reported-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> Tested-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> # SM8350-HDK
> Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> Signed-off-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> ---
One note below,
Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/msm/dp/dp_panel.c
> index a916b5f3b317..3777b1abacad 100644
> --- a/drivers/gpu/drm/msm/dp/dp_panel.c
> +++ b/drivers/gpu/drm/msm/dp/dp_panel.c
> @@ -90,22 +90,22 @@ static int dp_panel_read_dpcd(struct dp_panel *dp_panel)
> static u32 dp_panel_get_supported_bpp(struct dp_panel *dp_panel,
> u32 mode_edid_bpp, u32 mode_pclk_khz)
> {
> - struct dp_link_info *link_info;
> + const struct dp_link_info *link_info;
> const u32 max_supported_bpp = 30, min_supported_bpp = 18;
> - u32 bpp = 0, data_rate_khz = 0;
> + u32 bpp, data_rate_khz;
>
> bpp = min_t(u32, mode_edid_bpp, max_supported_bpp);
This can be min() because all types are u32.
>
> link_info = &dp_panel->link_info;
> data_rate_khz = link_info->num_lanes * link_info->rate * 8;
>
> - while (bpp > min_supported_bpp) {
> + do {
> if (mode_pclk_khz * bpp <= data_rate_khz)
> - break;
> + return bpp;
> bpp -= 6;
> - }
> + } while (bpp > min_supported_bpp);
>
> - return bpp;
> + return min_supported_bpp;
> }
>
> int dp_panel_read_sink_caps(struct dp_panel *dp_panel,
