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drm/i915/vblank: Add helper to get correct vblank length

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Currently crtc_vblank_start is assumed to be the vblank_start for the fixed
refresh rate case. That value can be different from the variable refresh
rate case whenever always_use_vrr_tg()==false. On icl/tgl it's always
different due to the extra vblank delay, and also on adl+ it could be
different if we were to use an optimized guardband.

So places where crtc_vblank_start is used to compute vblank length needs
change so as to account for cases where vrr is enabled. Specifically
with vrr.enable the effective vblank length is actually guardband.

Add a helper to get the correct vblank length for both vrr and fixed
refresh rate cases. Use this helper where vblank_start is used to
compute the vblank length.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/20251016055415.2101347-5-ankit.k.nautiyal@intel.com
This commit is contained in:
Ankit Nautiyal 2025-10-16 11:24:08 +05:30
parent 2cdcab0d3a
commit ca4edafa14
3 changed files with 14 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

10
drivers/gpu/drm/i915/display/intel_vblank.c
View file

@ -767,3 +767,13 @@ int intel_vblank_evade(struct intel_vblank_evade_ctx *evade)
return scanline;
}
int intel_crtc_vblank_length(const struct intel_crtc_state *crtc_state)
{
const struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
if (crtc_state->vrr.enable)
return crtc_state->vrr.guardband;
else
return adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
}

2
drivers/gpu/drm/i915/display/intel_vblank.h
View file

@ -48,4 +48,6 @@ const struct intel_crtc_state *
intel_pre_commit_crtc_state(struct intel_atomic_state *state,
struct intel_crtc *crtc);
int intel_crtc_vblank_length(const struct intel_crtc_state *crtc_state);
#endif /* __INTEL_VBLANK_H__ */

3
drivers/gpu/drm/i915/display/skl_watermark.c
View file

@ -28,6 +28,7 @@
#include "intel_flipq.h"
#include "intel_pcode.h"
#include "intel_plane.h"
#include "intel_vblank.h"
#include "intel_wm.h"
#include "skl_universal_plane_regs.h"
#include "skl_watermark.h"
@ -2241,7 +2242,7 @@ skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
scaler_prefill_latency(crtc_state) +
dsc_prefill_latency(crtc_state) +
wm0_lines >
adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
intel_crtc_vblank_length(crtc_state);
}
static int skl_max_wm0_lines(const struct intel_crtc_state *crtc_state)