[Intel-gfx] [PATCH 3/4] drm/i915: use ORIGIN_CPU for frontbuffer invalidation on WC mmaps

[Paulo Zanoni]

From: Chris Wilson <chris at chris-wilson.co.uk>

... instead of the previous ORIGIN_GTT. This should actually
invalidate FBC once something is written on the frontbuffer using WC
mmaps. The problem with ORIGIN_GTT is that the automatic hardware
tracking is not able to detect the WC writes as it can detect the GTT
writes.

This should help fix the SKL bug where nothing happens when you type
your username/password on lightdm.

This patch was originally pasted on an email by Chris and converted to
an actual git patch by Paulo.

v2 (From Paulo):
 - Make it a full variable instead of a bit-field (Daniel)
 - Use WRITE_ONCE (Chris)

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h |  6 ++++++
 drivers/gpu/drm/i915/i915_gem.c | 14 +++++++++++---
 2 files changed, 17 insertions(+), 3 deletions(-)

Chris, can you give your Signed-off-by on this patch, please?

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 53d9e3f..20a676d 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2204,6 +2204,12 @@ struct drm_i915_gem_object {
 
 	unsigned int frontbuffer_bits:INTEL_FRONTBUFFER_BITS;
 
+	/*
+	 * IMPORTANT: We have unlocked access to this, this must be a
+	 * stand-alone bool.
+	 */
+	unsigned int has_wc_mmap;
+
 	unsigned int pin_display;
 
 	struct sg_table *pages;
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index eae8d7a..98389e4 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1603,6 +1603,13 @@ static struct intel_rps_client *to_rps_client(struct drm_file *file)
 	return &fpriv->rps;
 }
 
+static enum fb_op_origin
+write_origin(struct drm_i915_gem_object *obj, unsigned domain)
+{
+	return domain == I915_GEM_DOMAIN_GTT && !obj->has_wc_mmap ?
+	       ORIGIN_GTT : ORIGIN_CPU;
+}
+
 /**
  * Called when user space prepares to use an object with the CPU, either
  * through the mmap ioctl's mapping or a GTT mapping.
@@ -1659,9 +1666,7 @@ i915_gem_set_domain_ioctl(struct drm_device *dev, void *data,
 		ret = i915_gem_object_set_to_cpu_domain(obj, write_domain != 0);
 
 	if (write_domain != 0)
-		intel_fb_obj_invalidate(obj,
-					write_domain == I915_GEM_DOMAIN_GTT ?
-					ORIGIN_GTT : ORIGIN_CPU);
+		intel_fb_obj_invalidate(obj, write_origin(obj, write_domain));
 
 unref:
 	drm_gem_object_unreference(&obj->base);
@@ -1768,6 +1773,9 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
 		else
 			addr = -ENOMEM;
 		up_write(&mm->mmap_sem);
+
+		/* This may race, but that's ok, it only gets set */
+		WRITE_ONCE(to_intel_bo(obj)->has_wc_mmap, true);
 	}
 	drm_gem_object_unreference_unlocked(obj);
 	if (IS_ERR((void *)addr))
-- 
2.5.5