[Intel-gfx] [PATCH 1/2] drm/i915: enable FBC on gen9+ too

[Paulo Zanoni]

Gen9+ platforms have been seeing a lot of screen flickerings and
underruns, so I never felt comfortable in enabling FBC on these
platforms since I didn't want to throw yet another feature on top of
the already complex problem. We now have code that automatically
disables FBC if we ever get an underrun, and the screen flickerings
seem to be mostly gone, so it may be a good time to try to finally
enable FBC by default on the newer platforms.

Besides, BDW FBC has been working fine over the year, which gives me a
little more confidence now.

For a little more information, please refer to commit a98ee79317b4
("drm/i915/fbc: enable FBC by default on HSW and BDW").

v2: Enable not only on SKL, but for everything new (Daniel).
v3: Rebase after the intel_sanitize_fbc_option() change.
v4: New rebase after 8 months, drop expired R-B tags.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
---
 drivers/gpu/drm/i915/intel_fbc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Daniel gave me a R-B for this patch maaaaany months ago, but I think
we can consider it as expired now.

QA just went through a round of testing and confirmed 100% pass rate
for SKL/KBL/BXT (VIZ-7181).

Besides, we do have at least one user with FBC enabled on SKL and
reporting possible issues, as we saw on #98213, which is already
fixed.

The problem that I've been discussing with Chris and Daniel is not a
user visible bug since it just keeps FBC deactivated if the client
doesn't issue the dirtyfb calls, and from what I can see, current user
space is fine.

I have a pending patch for an improvement on the CRTC-choosing code,
but that's not a bug fix and doesn't change how HSW+ behaves. It's
patch 2 of this series.

I think we can also consider reenabling FBC on HSW due to the
confirmation I got some time ago that the HSW regression is gone (both
bugs from c7f7e2feffb0 have confirmed that some patches that are
alredy merged fixed the problem without reverting HSW support). But
I won't propose this until we get to understand what's going on with
bug #99169.

diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
index 9aec63b..26a81a9 100644
--- a/drivers/gpu/drm/i915/intel_fbc.c
+++ b/drivers/gpu/drm/i915/intel_fbc.c
@@ -1317,7 +1317,7 @@ static int intel_sanitize_fbc_option(struct drm_i915_private *dev_priv)
 	if (!HAS_FBC(dev_priv))
 		return 0;
 
-	if (IS_BROADWELL(dev_priv))
+	if (IS_BROADWELL(dev_priv) || INTEL_GEN(dev_priv) >= 9)
 		return 1;
 
 	return 0;
-- 
2.7.4