Re: [PATCH v4 6/7] drm/i915/scaler: Check if vblank is sufficient for scaler

[Nautiyal, Ankit K]

On 1/8/2025 6:05 PM, Mitul Golani wrote:

Check if vblank is too short for scaler prefill latency.

Perhaps we can elaborate a bit.

Also add Bspec# in trailer.

--v2:
- Use hweight* family of functions for counting bits. [Jani]
- Update precision handling for hscale and vscale. [Ankit]
- Consider chroma downscaling factor during latency
calculation. [Ankit]
- Replace function name from scaler_prefill_time to
scaler_prefill_latency.

--v3:
- hscale_k and vscale_k values are already left shifted by 16,
after multiplying by 1000, those need to be right shifted to 16. [Ankit]
- Replace YCBCR444 to YCBCR420. [Ankit]
- Divide by 1000 * 1000 in end to get correct precision. [Ankit]
- Initialise latency to 0 to avoid any garbage.

Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.gol...@intel.com>
---
  drivers/gpu/drm/i915/display/skl_watermark.c | 31 ++++++++++++++++++++
  1 file changed, 31 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c 
b/drivers/gpu/drm/i915/display/skl_watermark.c
index f4458d1185b3..fe91854e456c 100644
--- a/drivers/gpu/drm/i915/display/skl_watermark.c
+++ b/drivers/gpu/drm/i915/display/skl_watermark.c
@@ -2292,6 +2292,36 @@ static int icl_build_plane_wm(struct intel_crtc_state 
*crtc_state,
        return 0;
  }

+static int

+scaler_prefill_latency(const struct intel_crtc_state *crtc_state)
+{
+       const struct intel_crtc_scaler_state *scaler_state =
+                                       &crtc_state->scaler_state;
+       int count = hweight32(scaler_state->scaler_users);
+       int latency = 0;
+       long long  hscale_k =
+               mul_u32_u32(scaler_state->scalers[0].hscale, 1000) >> 16;
+       long long vscale_k =
+               mul_u32_u32(scaler_state->scalers[0].vscale, 1000) >> 16;
+
+       if (!count)
+               return latency;
+
+       if (count > 1) {
+               int chroma_downscaling_factor =
+                       crtc_state->output_format == 
INTEL_OUTPUT_FORMAT_YCBCR420 ? 2 : 1;
+
+               latency = (4 * crtc_state->linetime) +
+                         (chroma_downscaling_factor *
+                          DIV_ROUND_UP_ULL((4 * crtc_state->linetime * 
hscale_k * vscale_k),
+                                           1000000));
+       } else {
+               latency = 4 * crtc_state->linetime;
+       }
+
+       return latency;
+}
+
  static bool
  skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
                        int wm0_lines, int latency)
@@ -2302,6 +2332,7 @@ skl_is_vblank_too_short(const struct intel_crtc_state 
*crtc_state,
        /* FIXME missing scaler and DSC pre-fill time */

The scaler part is addressed in this patch, so this can be removed.

Regards,

Ankit

        return crtc_state->framestart_delay +
                intel_usecs_to_scanlines(adjusted_mode, latency) +
+               scaler_prefill_latency(crtc_state) +
                wm0_lines >
                adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
  }