[PATCH v7 07/26] drm/i915/display: Handle vlv dsi workaround in scanline_in_safe_range too

Maarten Lankhorst
2026-03-10T11:57:38Z

Now that we have a macro, might as well handle the VLV dsi workaround
too.

This makes the vblank evasion code slightly more deterministic, by not
looping with interrupts disabled.

Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
---
drivers/gpu/drm/i915/display/intel_vblank.c | 36 ++++++++++-----------
1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c b/drivers/gpu/drm/i915/display/intel_vblank.c
index 73676d8ccec8b..3eb6418723a84 100644
--- a/drivers/gpu/drm/i915/display/intel_vblank.c
+++ b/drivers/gpu/drm/i915/display/intel_vblank.c
@@ -739,6 +739,24 @@ static bool scanline_in_safe_range(struct intel_vblank_evade_ctx *evade, int *sc
else
*scanline = __intel_get_crtc_scanline(evade->crtc);

+ /*
+ * On VLV/CHV DSI the scanline counter would appear to
+ * increment approx. 1/3 of a scanline before start of vblank.
+ * The registers still get latched at start of vblank however.
+ * This means we must not write any registers on the first
+ * line of vblank (since not the whole line is actually in
+ * vblank). And unfortunately we can't use the interrupt to
+ * wait here since it will fire too soon. We could use the
+ * frame start interrupt instead since it will fire after the
+ * critical scanline, but that would require more changes
+ * in the interrupt code. So for now we'll just do the nasty
+ * thing and poll for the bad scanline to pass us by.
+ *
+ * FIXME figure out if BXT+ DSI suffers from this as well
+ */
+ if (evade->need_vlv_dsi_wa && *scanline == evade->vblank_start)
+ return false;
+
return *scanline < evade->min || *scanline > evade->max;
}

@@ -769,24 +787,6 @@ int intel_vblank_evade(struct intel_vblank_evade_ctx *evade)
local_irq_disable();
}

- /*
- * On VLV/CHV DSI the scanline counter would appear to
- * increment approx. 1/3 of a scanline before start of vblank.
- * The registers still get latched at start of vblank however.
- * This means we must not write any registers on the first
- * line of vblank (since not the whole line is actually in
- * vblank). And unfortunately we can't use the interrupt to
- * wait here since it will fire too soon. We could use the
- * frame start interrupt instead since it will fire after the
- * critical scanline, but that would require more changes
- * in the interrupt code. So for now we'll just do the nasty
- * thing and poll for the bad scanline to pass us by.
- *
- * FIXME figure out if BXT+ DSI suffers from this as well
- */
- while (evade->need_vlv_dsi_wa && scanline == evade->vblank_start)
- scanline = intel_get_crtc_scanline(crtc);
-
return scanline;
}

--
2.51.0