[Intel-gfx] [PATCH] drm/i915: Pin the ifbdev for the info->system_base GGTT mmapping

[Daniel Vetter]

On Fri, Oct 23, 2015 at 10:17:44PM +0100, Dave Gordon wrote:
> On 08/10/15 21:50, Wayne Boyer wrote:
> >From: Chris Wilson <chris at chris-wilson.co.uk>
> >
> >A long time ago (before 3.14) we relied on a permanent pinning of the
> >ifbdev to lock the fb in place inside the GGTT. However, the
> >introduction of stealing the BIOS framebuffer and reusing its address in
> >the GGTT for the fbdev has muddied waters and we use an inherited fb.
> >However, the inherited fb is only pinned whilst it is active and we no
> >longer have an explicit pin for the info->system_base mmapping used by
> >the fbdev. The result is that after some aperture pressure the fbdev may
> >be evicted, but we continue to write the fbcon into the same GGTT
> >address - overwriting anything else that may be put into that offset.
> >The effect is most pronounced across suspend/resume as
> >intel_fbdev_set_suspend() does a full clear over the whole scanout.
> >
> >v2: rebased on latest nightly (Wayne)
> >v3: changed i915_gem_object_ggtt_pin() to i915_gem_obj_ggtt_pin() based
> >on Chris' review. (Wayne)
> >
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >Cc: "Goel, Akash" <akash.goel at intel.com>
> >Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> >Cc: Jesse Barnes <jbarnes at virtuousgeek.org>
> >Cc: stable at vger.kernel.org
> >Reviewed-by: Deepak S <deepak.s at linux.intel.com>
> >Signed-off-by: Wayne Boyer <wayne.boyer at intel.com>
> >---
> >  drivers/gpu/drm/i915/intel_fbdev.c | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> >
> >diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> >index 6532912..0ad46521 100644
> >--- a/drivers/gpu/drm/i915/intel_fbdev.c
> >+++ b/drivers/gpu/drm/i915/intel_fbdev.c
> >@@ -215,6 +215,16 @@ static int intelfb_create(struct drm_fb_helper *helper,
> >  	obj = intel_fb->obj;
> >  	size = obj->base.size;
> >
> >+	/* The fb constructor will have already pinned us (or inherited a
> >+	 * GGTT region from the BIOS) suitable for a scanout, so
> >+	 * this should just be a no-op and increment the pin count for the
> >+	 * fbdev mmapping. It does have a useful side-effect of validating
> >+	 * the pin for fbdev's use via a GGTT mmapping.
> >+	 */
> >+	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
> >+	if (ret)
> >+		goto out_unlock;
> >+
> >  	info = drm_fb_helper_alloc_fbi(helper);
> >  	if (IS_ERR(info)) {
> >  		ret = PTR_ERR(info);
> >@@ -274,6 +284,9 @@ static int intelfb_create(struct drm_fb_helper *helper,
> >  out_destroy_fbi:
> >  	drm_fb_helper_release_fbi(helper);
> >  out_unpin:
> >+	/* Once for info->screen_base mmaping... */
> >+	i915_gem_object_ggtt_unpin(obj);
> >+	/* ...and once for the intel_fb */
> >  	i915_gem_object_ggtt_unpin(obj);
> >  	drm_gem_object_unreference(&obj->base);
> >  out_unlock:
> >@@ -514,6 +527,8 @@ static const struct drm_fb_helper_funcs intel_fb_helper_funcs = {
> >  static void intel_fbdev_destroy(struct drm_device *dev,
> >  				struct intel_fbdev *ifbdev)
> >  {
> >+	/* Release the pinning for the info->screen_base mmaping. */
> >+	i915_gem_object_ggtt_unpin(ifbdev->fb->obj);
> >
> >  	drm_fb_helper_unregister_fbi(&ifbdev->helper);
> >  	drm_fb_helper_release_fbi(&ifbdev->helper);
> 
> Hmm .. pinning now done by i915_gem_obj_ggtt_pin(), but the unpinning
> function is i915_gem_object_ggtt_unpin(). Just the sort of asymmetry that
> helps everyone understand what's going on :(
> 
> Could we not have a mass rename of the various i915_gem_obj{ect} functions
> to ONE consistent naming convention? (Personally I prefer 'obj' because it's
> shorter, but consistency is more important than saving just 3 letters).

Of course, just needs someone to do it, and make sure to not step onto too
many toes. I'd love if more people actually take charge of gem instead of
piling more on top.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch