[Intel-gfx] [PATCH v2 2/6] drm/i915: Fix bw atomic check when switching between SAGV vs. no SAGV

[Ville Syrjala <ville.syrjala@linux.intel.com>]

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

If the only thing that is changing is SAGV vs. no SAGV but
the number of active planes and the total data rates end up
unchanged we currently bail out of intel_bw_atomic_check()
early and forget to actually compute the new WGV point
mask and thus won't actually enable/disable SAGV as requested.
This ends up poorly if we end up running with SAGV enabled
when we shouldn't. Usually ends up in underruns.
To fix this let's go through the QGV point mask computation
if anyone else already added the bw state for us.

Cc: stable@vger.kernel.org
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Fixes: 20f505f22531 ("drm/i915: Restrict qgv points which don't have enough bandwidth.")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_bw.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_bw.c b/drivers/gpu/drm/i915/display/intel_bw.c
index 23aa8e06de18..d72ccee7d53b 100644
--- a/drivers/gpu/drm/i915/display/intel_bw.c
+++ b/drivers/gpu/drm/i915/display/intel_bw.c
@@ -846,6 +846,13 @@ int intel_bw_atomic_check(struct intel_atomic_state *state)
 	if (num_psf_gv_points > 0)
 		mask |= REG_GENMASK(num_psf_gv_points - 1, 0) << ADLS_PSF_PT_SHIFT;
 
+	/*
+	 * If we already have the bw state then recompute everything
+	 * even if pipe data_rate / active_planes didn't change.
+	 * Other things (such as SAGV) may have changed.
+	 */
+	new_bw_state = intel_atomic_get_new_bw_state(state);
+
 	for_each_oldnew_intel_crtc_in_state(state, crtc, old_crtc_state,
 					    new_crtc_state, i) {
 		unsigned int old_data_rate =
-- 
2.34.1