[PATCH 6.18 027/333] drm/msm/dsi: fix hdisplay calculation when programming dsi registers

Greg Kroah-Hartman
2026-03-17T17:06:00Z

From: Pengyu Luo <mitltlatltl@gmail.com>

[ Upstream commit ac47870fd795549f03d57e0879fc730c79119f4b ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/msm/dsi/dsi_host.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index e0de545d40775..e8e83ee61eb09 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;
--
2.51.0