Hi Chris,
On Fri, Dec 04, 2015 at 04:05:26PM +0000, Chris Wilson wrote:
> 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: Only unpin the intel_fb is we allocate it. If we inherit the fb from
> the BIOS, we do not own the pinned vma (except for the reference we add
> in this patch for our access via info->screen_base).
>
> v3: Finish balancing the vma pinning for the normal !preallocated case.
>
> v4: Try to simplify the pinning even further.
> v5: Leak the VMA (cleaned up by object-free) to avoid complicated error paths.
It's beautiful how little code is needed to fix this. The only remaining
thing I noticed now while looking over the error paths is that these
lines in intelfb_alloc() become obsolete with your patch:
out:
mutex_unlock(&dev->struct_mutex);
- if (!IS_ERR_OR_NULL(fb))
- drm_framebuffer_unreference(fb);
return ret;
}
Because at each of the remaining "goto out" in the function,
fb can be only either an ERR_PTR or NULL.
Also, further up in the function, the declaration of fb can then be
changed thus:
- struct drm_framebuffer *fb = NULL;
+ struct drm_framebuffer *fb;
Kind regards,
Lukas
>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: "Goel, Akash" <akash.g...@intel.com>
> Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
> Cc: Jesse Barnes <jbar...@virtuousgeek.org>
> Cc: Lukas Wunner <lu...@wunner.de>
> Cc: stable@vger.kernel.org
> ---
> drivers/gpu/drm/i915/intel_fbdev.c | 20 +++++++++++++-------
> 1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c
> b/drivers/gpu/drm/i915/intel_fbdev.c
> index 7ccde58f8c98..bea75cafc623 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -163,13 +163,6 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
> goto out;
> }
>
> - /* Flush everything out, we'll be doing GTT only from now on */
> - ret = intel_pin_and_fence_fb_obj(NULL, fb, NULL);
> - if (ret) {
> - DRM_ERROR("failed to pin obj: %d\n", ret);
> - goto out;
> - }
> -
> mutex_unlock(&dev->struct_mutex);
>
> ifbdev->fb = to_intel_framebuffer(fb);
> @@ -225,6 +218,14 @@ static int intelfb_create(struct drm_fb_helper *helper,
>
> mutex_lock(&dev->struct_mutex);
>
> + /* Pin the GGTT vma for our access via info->screen_base.
> + * This also validates that any existing fb inherited from the
> + * BIOS is suitable for own access.
> + */
> + ret = intel_pin_and_fence_fb_obj(NULL, &ifbdev->fb->base, NULL);
> + if (ret)
> + goto out_unlock;
> +
> info = drm_fb_helper_alloc_fbi(helper);
> if (IS_ERR(info)) {
> DRM_ERROR("Failed to allocate fb_info\n");
> @@ -287,6 +288,7 @@ out_destroy_fbi:
> drm_fb_helper_release_fbi(helper);
> out_unpin:
> i915_gem_object_ggtt_unpin(obj);
> +out_unlock:
> mutex_unlock(&dev->struct_mutex);
> return ret;
> }
> @@ -524,6 +526,10 @@ static const struct drm_fb_helper_funcs
> intel_fb_helper_funcs = {
> static void intel_fbdev_destroy(struct drm_device *dev,
> struct intel_fbdev *ifbdev)
> {
> + /* We rely on the object-free to release the VMA pinning for
> + * the info->screen_base mmaping. Leaking the VMA is simpler than
> + * trying to rectify all the possible error paths leading here.
> + */
>
> drm_fb_helper_unregister_fbi(&ifbdev->helper);
> drm_fb_helper_release_fbi(&ifbdev->helper);
> --
> 2.6.2
>
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