On 12/22/2025 6:26 PM, Imre Deak wrote:
On Mon, Dec 22, 2025 at 10:14:43AM +0530, Ankit Nautiyal wrote:
When DSC is enabled on a pipe, the pipe pixel rate input to the
CDCLK frequency and pipe joining calculation needs an adjustment to
account for compression overhead "bubbles" added at each horizontal
slice boundary.
Account for this overhead while computing min cdclk required for DSC.
v2: Get rid of the scaling factor and return unchanged pixel-rate
instead of 0.
Bspec:68912
Signed-off-by: Ankit Nautiyal <[email protected]>
---
drivers/gpu/drm/i915/display/intel_vdsc.c | 45 +++++++++++++++++++++--
1 file changed, 41 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.c
b/drivers/gpu/drm/i915/display/intel_vdsc.c
index ad5fe841e4b3..b91cd009be9d 100644
--- a/drivers/gpu/drm/i915/display/intel_vdsc.c
+++ b/drivers/gpu/drm/i915/display/intel_vdsc.c
@@ -1050,15 +1050,52 @@ void intel_vdsc_state_dump(struct drm_printer *p, int
indent,
drm_dsc_dump_config(p, indent, &crtc_state->dsc.config);
}
+static
+int intel_dsc_get_pixel_rate_with_dsc_bubbles(int pixel_rate, int htotal,
+ int dsc_horizontal_slices)
+{
+ int dsc_slice_bubbles;
+ u64 num;
+
+ if (!htotal)
Should this also warn as !slice_width below?
Yeah can add add warn here..
+ return pixel_rate;
+
+ dsc_slice_bubbles = 14 * dsc_horizontal_slices;
+ num = (u64)pixel_rate * (u64)(htotal + dsc_slice_bubbles);
Better to use mul_u32_u32() to avoid the casts and 64-bit x 64-bit
multiplication.
Ok sure will use mul_u32_u32 to avoid casts here.
+
+ return (int)DIV_ROUND_UP_ULL(num, (u64)htotal);
Both casts are ensured by the compiler already, so no need for doing
them explicitly.
Got it.
+}
+
+static
+int pixel_rate_with_dsc_bubbles(const struct intel_crtc_state *crtc_state, int
pixel_rate)
+{
+ struct intel_display *display = to_intel_display(crtc_state);
+ const struct drm_display_mode *adjusted_mode =
&crtc_state->hw.adjusted_mode;
+ const struct drm_dsc_config *vdsc_cfg = &crtc_state->dsc.config;
+ int dsc_horizontal_slices;
+
+ if (drm_WARN_ON(display->drm, !vdsc_cfg->slice_width))
+ return pixel_rate;
+
+ dsc_horizontal_slices = vdsc_cfg->pic_width / vdsc_cfg->slice_width;
The above looks to be the same as crtc_state->dsc.slice_count, aka the
slices per scanline, could you use that instead?
Apparently we are not filling dsc.slice_count. We are filling
dsc.slice_width and the pic_width.
This parameter seems to be unused, perhaps can be dropped?
Regards,
Ankit
+
+ return intel_dsc_get_pixel_rate_with_dsc_bubbles(pixel_rate,
+
adjusted_mode->crtc_htotal,
+ dsc_horizontal_slices);
+}
+
int intel_vdsc_min_cdclk(const struct intel_crtc_state *crtc_state)
{
struct intel_display *display = to_intel_display(crtc_state);
int num_vdsc_instances = intel_dsc_get_num_vdsc_instances(crtc_state);
+ int pixel_rate;
int min_cdclk;
if (!crtc_state->dsc.compression_enable)
return 0;
+ pixel_rate = pixel_rate_with_dsc_bubbles(crtc_state, crtc_state->pixel_rate);
+
/*
* When we decide to use only one VDSC engine, since
* each VDSC operates with 1 ppc throughput, pixel clock
@@ -1066,7 +1103,7 @@ int intel_vdsc_min_cdclk(const struct intel_crtc_state
*crtc_state)
* If there 2 VDSC engines, then pixel clock can't be higher than
* VDSC clock(cdclk) * 2 and so on.
*/
- min_cdclk = DIV_ROUND_UP(crtc_state->pixel_rate, num_vdsc_instances);
+ min_cdclk = DIV_ROUND_UP(pixel_rate, num_vdsc_instances);
if (crtc_state->joiner_pipes) {
int pixel_clock =
intel_dp_mode_to_fec_clock(crtc_state->hw.adjusted_mode.clock);
@@ -1084,9 +1121,9 @@ int intel_vdsc_min_cdclk(const struct intel_crtc_state
*crtc_state)
* => CDCLK >= compressed_bpp * Pixel clock / 2 * Bigjoiner
Interface bits
*/
int bigjoiner_interface_bits = DISPLAY_VER(display) >= 14 ? 36
: 24;
- int min_cdclk_bj =
-
(fxp_q4_to_int_roundup(crtc_state->dsc.compressed_bpp_x16) *
- pixel_clock) / (2 * bigjoiner_interface_bits);
+ int adjusted_pixel_rate =
pixel_rate_with_dsc_bubbles(crtc_state, pixel_clock);
+ int min_cdclk_bj =
(fxp_q4_to_int_roundup(crtc_state->dsc.compressed_bpp_x16) *
+ adjusted_pixel_rate) / (2 *
bigjoiner_interface_bits);
min_cdclk = max(min_cdclk, min_cdclk_bj);
}
--
2.45.2
