Re: [RFC v2 5/6] drm/i915/scaler: Check if vblank is sufficient for scaler

[Nautiyal, Ankit K]

On 12/17/2024 11:37 PM, Mitul Golani wrote:
Check if vblank is too short for scaler prefill latency.

Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.gol...@intel.com>
---
  drivers/gpu/drm/i915/display/skl_watermark.c | 22 ++++++++++++++++++++
  1 file changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c 
b/drivers/gpu/drm/i915/display/skl_watermark.c
index d3506e8ccd9b..a538e2b82c12 100644
--- a/drivers/gpu/drm/i915/display/skl_watermark.c
+++ b/drivers/gpu/drm/i915/display/skl_watermark.c
@@ -2292,6 +2292,27 @@ static int icl_build_plane_wm(struct intel_crtc_state 
*crtc_state,
        return 0;
  }
  
+static int
+scaler_prefill_time(const struct intel_crtc_state *crtc_state)
+{
+       const struct intel_crtc_scaler_state *scaler_state =
+                                       &crtc_state->scaler_state;
+       int scaler_users = scaler_state->scaler_users;
+       int count = 0;
+       int hscale = scaler_state->scalers[0].hscale;
+       int vscale = scaler_state->scalers[0].vscale;
+
+       while (scaler_users) {
+               count += scaler_users & 1;
+               scaler_users >>= 1;
+       }
+
+       if (count > 1)
+               return (4 * crtc_state->linetime * hscale * vscale);

This will not work. We need to take proper precision into account to do 
this calculation.

currently hscale,vscale are left shifted by 16.

Regards,

Ankit

+       else
+               return (4 * crtc_state->linetime);
+}
+
  static bool
  skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
                        int wm0_lines, int latency)
@@ -2302,6 +2323,7 @@ skl_is_vblank_too_short(const struct intel_crtc_state 
*crtc_state,
        /* FIXME missing scaler and DSC pre-fill time */
        return crtc_state->framestart_delay +
                intel_usecs_to_scanlines(adjusted_mode, latency) +
+               scaler_prefill_time(crtc_state) +
                wm0_lines >
                adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
  }