[PATCH RFC] drm/msm/dpu: calculate data_width like downstream

[Alexander Koskovich <akoskovich@pm.me>]

Derive INTF data_width from dce_bytes_per_line rather than
timing->width when DSC is enabled. Use DIV_ROUND_UP to avoid
rounding errors.

Signed-off-by: Alexander Koskovich <akoskovich@pm.me>
---
This patch changes the data_width calculation to match downstream,
and avoids needing to change the divisor for timing->width to /24.

However I am not sure if this is a correct approach, but at least
with this I get the same values for data_width as downstream now:

data_width w/ no widebus
before: 288
after: 360

data_with w/ widebus
before: 144
after: 180

This was tested with the BOE BF068MWM-TD0 on the Nothing Phone (3a),
it would be greatly appreciated if someone from QCOM could weigh in
on if this is a correct approach.

Tested with kmscube and getting 120FPS, also note that this was
tested with a few other changes:

(drm/msm/dsi: fix hdisplay calculation when programming dsi registers)
(drm/msm/dsi: fix pclk rate calculation for bonded dsi)
(drm/msm/dsi: fix bits_per_pclk)
(drm/msm/dsi: fix hdisplay calculation for CMD mode panel)
---
 .../gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c   |  2 ++
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c        | 23 +++++++++++++++++-----
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h        |  1 +
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
index 0ba777bda253..ba810f26ea30 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
@@ -10,6 +10,7 @@
 #include "dpu_formats.h"
 #include "dpu_trace.h"
 #include "disp/msm_disp_snapshot.h"
+#include "msm_dsc_helper.h"
 
 #include <drm/display/drm_dsc_helper.h>
 #include <drm/drm_managed.h>
@@ -136,6 +137,7 @@ static void drm_mode_to_intf_timing_params(
 		timing->width = timing->width * drm_dsc_get_bpp_int(dsc) /
 				(dsc->bits_per_component * 3);
 		timing->xres = timing->width;
+		timing->dce_bytes_per_line = msm_dsc_get_bytes_per_line(dsc);
 	}
 }
 
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
index 7e620f590984..de6b5b0f70c4 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
@@ -173,13 +173,26 @@ static void dpu_hw_intf_setup_timing_engine(struct dpu_hw_intf *intf,
 	data_width = p->width;
 
 	/*
-	 * If widebus is enabled, data is valid for only half the active window
-	 * since the data rate is doubled in this mode. But for the compression
-	 * mode in DP case, the p->width is already adjusted in
-	 * drm_mode_to_intf_timing_params()
+	 * If widebus is disabled:
+	 * For uncompressed stream, the data is valid for the entire active
+	 * window period.
+	 * For compressed stream, data is valid for a shorter time period
+	 * inside the active window depending on the compression ratio.
+	 *
+	 * If widebus is enabled:
+	 * For uncompressed stream, data is valid for only half the active
+	 * window, since the data rate is doubled in this mode.
+	 * For compressed stream, data validity window needs to be adjusted for
+	 * compression ratio and then further halved.
 	 */
-	if (p->wide_bus_en && !dp_intf)
+	if (p->compression_en && !dp_intf) {
+		if (p->wide_bus_en)
+			data_width = DIV_ROUND_UP(p->dce_bytes_per_line, 6);
+		else
+			data_width = DIV_ROUND_UP(p->dce_bytes_per_line, 3);
+	} else if (p->wide_bus_en && !dp_intf) {
 		data_width = p->width >> 1;
+	}
 
 	/* TODO: handle DSC+DP case, we only handle DSC+DSI case so far */
 	if (p->compression_en && !dp_intf &&
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h
index f6ef2c21b66d..badd26305fc9 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h
@@ -35,6 +35,7 @@ struct dpu_hw_intf_timing_params {
 
 	bool wide_bus_en;
 	bool compression_en;
+	u32 dce_bytes_per_line;
 };
 
 struct dpu_hw_intf_prog_fetch {

---
base-commit: f338e77383789c0cae23ca3d48adcc5e9e137e3c
change-id: 20260322-fix-data-width-calc-c44287df08b8

Best regards,
-- 
Alexander Koskovich <akoskovich@pm.me>