drm/msm/dp: fix the max supported bpp logic

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

changes in v3:
	- replace min_t with just min as all params are u32

Fixes: c943b49 ("drm/msm/dp: add displayPort driver support")
Reported-by: Dmitry Baryshkov <[email protected]>
Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/43
Tested-by: Dmitry Baryshkov <[email protected]> # SM8350-HDK
Reviewed-by: Stephen Boyd <[email protected]>
Patchwork: https://patchwork.freedesktop.org/patch/607073/
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Stephen Boyd <[email protected]>
Signed-off-by: Abhinav Kumar <[email protected]>

Author: Abhinav Kumar

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);
+	bpp = min(mode_edid_bpp, max_supported_bpp);
 
 	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,
@@ -423,8 +423,9 @@ int dp_panel_init_panel_info(struct dp_panel *dp_panel)
 				drm_mode->clock);
 	drm_dbg_dp(panel->drm_dev, "bpp = %d\n", dp_panel->dp_mode.bpp);
 
-	dp_panel->dp_mode.bpp = max_t(u32, 18,
-				min_t(u32, dp_panel->dp_mode.bpp, 30));
+	dp_panel->dp_mode.bpp = dp_panel_get_mode_bpp(dp_panel, dp_panel->dp_mode.bpp,
+						      dp_panel->dp_mode.drm_mode.clock);
+
 	drm_dbg_dp(panel->drm_dev, "updated bpp = %d\n",
 				dp_panel->dp_mode.bpp);