From: Pengyu Luo <mitltlatltl@gmail.com>
Date: Sat, 14 Feb 2026 10:51:28 +0000 (+0800)
Subject: drm/msm/dsi: fix hdisplay calculation when programming dsi registers
X-Git-Tag: v7.0-rc4~17^2~4^2~8
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ac47870fd795549f03d57e0879fc730c79119f4b;p=thirdparty%2Fkernel%2Flinux.git

drm/msm/dsi: fix hdisplay calculation when programming dsi registers

Recently, the hdisplay calculation is working for 3:1 compressed ratio
only. If we have a video panel with DSC BPP = 8, and BPC = 10, we still
use the default bits_per_pclk = 24, then we get the wrong hdisplay. We
can draw the conclusion by cross-comparing the calculation with the
calculation in dsi_adjust_pclk_for_compression().

Since CMD mode does not use this, we can remove
!(msm_host->mode_flags & MIPI_DSI_MODE_VIDEO) safely.

Fixes: efcbd6f9cdeb ("drm/msm/dsi: Enable widebus for DSI")
Signed-off-by: Pengyu Luo <mitltlatltl@gmail.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/704822/
Link: https://lore.kernel.org/r/20260214105145.105308-1-mitltlatltl@gmail.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index e0de545d4077..e8e83ee61eb0 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -993,7 +993,7 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
 
 	if (msm_host->dsc) {
 		struct drm_dsc_config *dsc = msm_host->dsc;
-		u32 bytes_per_pclk;
+		u32 bits_per_pclk;
 
 		/* update dsc params with timing params */
 		if (!dsc || !mode->hdisplay || !mode->vdisplay) {
@@ -1015,7 +1015,9 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
 
 		/*
 		 * DPU sends 3 bytes per pclk cycle to DSI. If widebus is
-		 * enabled, bus width is extended to 6 bytes.
+		 * enabled, MDP always sends out 48-bit compressed data per
+		 * pclk and on average, DSI consumes an amount of compressed
+		 * data equivalent to the uncompressed pixel depth per pclk.
 		 *
 		 * Calculate the number of pclks needed to transmit one line of
 		 * the compressed data.
@@ -1027,12 +1029,12 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
 		 * unused anyway.
 		 */
 		h_total -= hdisplay;
-		if (wide_bus_enabled && !(msm_host->mode_flags & MIPI_DSI_MODE_VIDEO))
-			bytes_per_pclk = 6;
+		if (wide_bus_enabled)
+			bits_per_pclk = mipi_dsi_pixel_format_to_bpp(msm_host->format);
 		else
-			bytes_per_pclk = 3;
+			bits_per_pclk = 24;
 
-		hdisplay = DIV_ROUND_UP(msm_dsc_get_bytes_per_line(msm_host->dsc), bytes_per_pclk);
+		hdisplay = DIV_ROUND_UP(msm_dsc_get_bytes_per_line(msm_host->dsc) * 8, bits_per_pclk);
 
 		h_total += hdisplay;
 		ha_end = ha_start + hdisplay;