Re: [PATCH 06/19] drm/i915/display: Account for DSC not split case while computing cdclk

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On 7/20/2023 2:46 PM, Lisovskiy, Stanislav wrote:
On Thu, Jul 13, 2023 at 04:03:33PM +0530, Ankit Nautiyal wrote:
Currently we assume 2 Pixels Per Clock (PPC) while computing
plane cdclk and min_cdlck. In cases where DSC single engine
is used the throughput is 1 PPC.

So account for the above case, while computing cdclk.

v2: Use helper to get the adjusted pixel rate.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>
---
  drivers/gpu/drm/i915/display/intel_cdclk.c         |  2 +-
  drivers/gpu/drm/i915/display/intel_vdsc.c          | 12 ++++++++++++
  drivers/gpu/drm/i915/display/intel_vdsc.h          |  2 ++
  drivers/gpu/drm/i915/display/skl_universal_plane.c |  4 ++--
  4 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
index dcc1f6941b60..701909966545 100644
--- a/drivers/gpu/drm/i915/display/intel_cdclk.c
+++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
@@ -2508,7 +2508,7 @@ static int intel_pixel_rate_to_cdclk(const struct intel_crtc_state *crtc_state)
  	int pixel_rate = crtc_state->pixel_rate;
if (DISPLAY_VER(dev_priv) >= 10)
-		return DIV_ROUND_UP(pixel_rate, 2);
+		return intel_dsc_get_adjusted_pixel_rate(crtc_state, pixel_rate);
  	else if (DISPLAY_VER(dev_priv) == 9 ||
  		 IS_BROADWELL(dev_priv) || IS_HASWELL(dev_priv))
  		return pixel_rate;
diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.c b/drivers/gpu/drm/i915/display/intel_vdsc.c
index 9d76c2756784..bbfdbf06da68 100644
--- a/drivers/gpu/drm/i915/display/intel_vdsc.c
+++ b/drivers/gpu/drm/i915/display/intel_vdsc.c
@@ -1038,3 +1038,15 @@ void intel_dsc_get_config(struct intel_crtc_state *crtc_state)
  out:
  	intel_display_power_put(dev_priv, power_domain, wakeref);
  }
+
+int intel_dsc_get_adjusted_pixel_rate(const struct intel_crtc_state *crtc_state, int pixel_rate)
+{
+	/*
+	 * If single VDSC engine is used, it uses one pixel per clock
+	 * otherwise we use two pixels per clock.
+	 */
+	if (crtc_state->dsc.compression_enable && !crtc_state->dsc.dsc_split)
+		return pixel_rate;
+
+	return DIV_ROUND_UP(pixel_rate, 2);
+}
diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.h b/drivers/gpu/drm/i915/display/intel_vdsc.h
index 2cc41ff08909..3bb4b1980b6b 100644
--- a/drivers/gpu/drm/i915/display/intel_vdsc.h
+++ b/drivers/gpu/drm/i915/display/intel_vdsc.h
@@ -28,4 +28,6 @@ void intel_dsc_dsi_pps_write(struct intel_encoder *encoder,
  void intel_dsc_dp_pps_write(struct intel_encoder *encoder,
  			    const struct intel_crtc_state *crtc_state);
+int intel_dsc_get_adjusted_pixel_rate(const struct intel_crtc_state *crtc_state, int pixel_rate);
+
  #endif /* __INTEL_VDSC_H__ */
diff --git a/drivers/gpu/drm/i915/display/skl_universal_plane.c b/drivers/gpu/drm/i915/display/skl_universal_plane.c
index 6b01a0b68b97..9eeb25ec4be9 100644
--- a/drivers/gpu/drm/i915/display/skl_universal_plane.c
+++ b/drivers/gpu/drm/i915/display/skl_universal_plane.c
@@ -17,6 +17,7 @@
  #include "intel_fb.h"
  #include "intel_fbc.h"
  #include "intel_psr.h"
+#include "intel_vdsc.h"
  #include "skl_scaler.h"
  #include "skl_universal_plane.h"
  #include "skl_watermark.h"
@@ -263,8 +264,7 @@ static int icl_plane_min_cdclk(const struct intel_crtc_state *crtc_state,
  {
  	unsigned int pixel_rate = intel_plane_pixel_rate(crtc_state, plane_state);
- /* two pixels per clock */
-	return DIV_ROUND_UP(pixel_rate, 2);
+	return intel_dsc_get_adjusted_pixel_rate(crtc_state, pixel_rate);
Hi Ankit,

I think the thing what you are taking of is already handled here in intel_cdclk.c:

	/*
          * When we decide to use only one VDSC engine, since
          * each VDSC operates with 1 ppc throughput, pixel clock
          * cannot be higher than the VDSC clock (cdclk)
          * If there 2 VDSC engines, then pixel clock can't be higher than
          * VDSC clock(cdclk) * 2 and so on.
          */
         if (crtc_state->dsc.compression_enable) {
                 int num_vdsc_instances = intel_dsc_get_num_vdsc_instances(crtc_state);

                 min_cdclk = max_t(int, min_cdclk,
                                   DIV_ROUND_UP(crtc_state->pixel_rate,
                                                num_vdsc_instances));
         }

As far as I understand this condition is coming from the pixel clock limitation as an input to the splitter (Bspec: 49259):

Pipe BW check:

Pixel clock < PPC * CDCLK frequency * Number of pipes joined

PPC = 1 or 2 depending on number of DSC engines used within the pipe.

So it implies CDCLK frequency > Pixel clock / (PPC * Number of pipes joined)

num_vdsc_instances is actually giving us (PPC * number of pipes joined).


I completely agree that there will be no effect of the change on the min_cdclk that gets computed in any case, whether DSC, 1 engine, 2 engine,  bigjoiner or no DSC.

Only thing is for the case where 1 DSC engine is used, what intel_pixel_rate_to_cdclk return will be different, and its due to the fact that pipe is driven with 1PPC.

But as I said, the min_cdclk computed will be same as without patch. So we can certainly do away with this change, and I can drop this from the patch.


But in case of icl_plane_min_cdclk, currently we are dividing the plane_pixel_rate by 2, citing that we use 2 pixel per clock, to get the plane_min_cdclk.

Should this not be 1 PPC in case where single DSC engine is used? In that case plane_min_cdclk will be double. Should we keep the change only for plane_min_cdclk then?


Regards,

Ankit



Also even if something still have to be done here, I think we should preferrably
deal with anything related to DSC in a single place, to prevent any kind of
confusion(when those checks are scattered in different places, it is way more easy to forget/not notice something)

I think intel_pixel_rate_to_cdclk isn't supposed to know anything about DSC or any other specifics like audio checks and etc - it is
just dealing with the "default" uncompressed case.
Any other additional limitations or checks we apply after those, as there are
quite many anyway.

Stan


  }
static void
--
2.40.1




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