Another observation that occurred to me only after sending away my
previous message (sorry):
On Thu, Oct 08, 2015 at 01:50:21PM -0700, Wayne Boyer wrote:
> From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>
> 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.
Since this only concerns the case when the fb was inherited from BIOS,
why don't you invoke i915_gem_obj_ggtt_pin() only in this particular case?
It's discernible from the prealloc variable.
I think then you also don't need to call i915_gem_object_ggtt_unpin() twice.
>
> 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@xxxxxxxxxxxxxxxxxx>
> Cc: "Goel, Akash" <akash.goel@xxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Reviewed-by: Deepak S <deepak.s@xxxxxxxxxxxxxxx>
> Signed-off-by: Wayne Boyer <wayne.boyer@xxxxxxxxx>
> ---
> 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);
> --
> 1.9.1
>
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