On Tue, Dec 13, 2016 at 05:57:26PM -0200, Paulo Zanoni wrote:
> Reserve the first page of stolen memory right after initializing the
> mm allocator. This means that we won't inherit the FB in case the BIOS
> decides to put it at the start of stolen. IMHO, avoiding constant
> screen flickering is more important than BIOS framebuffer inheritance.
>
> TODO: the goal is to ask everybody with screen flickering problems to
> test this patch. Hopefully we'll be able to add a bunch of Bugzilla
> tags here before merging it.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94605
> Cc: sta...@vger.kernel.org
> Signed-off-by: Paulo Zanoni <paulo.r.zan...@intel.com>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 3 +++
> drivers/gpu/drm/i915/i915_gem_stolen.c | 30 +++++++++++++-----------------
> 2 files changed, 16 insertions(+), 17 deletions(-)
>
>
> Time to spam bugzilla again with links to patchwork. The tester on
> fd.o bug 94605 suggests this may be the fix we've been looking for.
>
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 0e11ed7..0868a88 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1531,6 +1531,9 @@ struct i915_gem_mm {
> /** LRU list of objects with fence regs on them. */
> struct list_head fence_list;
>
> + /** First page of stolen, for platforms where it's reserved. */
> + struct drm_mm_node first_page;
> +
> /**
> * Are we in a non-interruptible section of code like
> * modesetting?
> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c
> b/drivers/gpu/drm/i915/i915_gem_stolen.c
> index b1c8897..9b3ae58 100644
> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> @@ -54,12 +54,6 @@ int i915_gem_stolen_insert_node_in_range(struct
> drm_i915_private *dev_priv,
> if (!drm_mm_initialized(&dev_priv->mm.stolen))
> return -ENODEV;
>
> - /* See the comment at the drm_mm_init() call for more about this check.
> - * WaSkipStolenMemoryFirstPage:bdw+ (incomplete)
> - */
> - if (start < 4096 && INTEL_GEN(dev_priv) >= 8)
> - start = 4096;
> -
> mutex_lock(&dev_priv->mm.stolen_lock);
> ret = drm_mm_insert_node_in_range(&dev_priv->mm.stolen, node, size,
> alignment, start, end,
> @@ -286,6 +280,9 @@ void i915_gem_cleanup_stolen(struct drm_device *dev)
> if (!drm_mm_initialized(&dev_priv->mm.stolen))
> return;
>
> + if (drm_mm_node_allocated(&dev_priv->mm.first_page))
> + drm_mm_remove_node(&dev_priv->mm.first_page);
> +
> drm_mm_takedown(&dev_priv->mm.stolen);
> }
>
> @@ -491,19 +488,18 @@ int i915_gem_init_stolen(struct drm_i915_private
> *dev_priv)
>
> ggtt->stolen_usable_size = ggtt->stolen_size - reserved_total;
>
> - /*
> - * Basic memrange allocator for stolen space.
> - *
> - * TODO: Notice that some platforms require us to not use the first page
> - * of the stolen memory but their BIOSes may still put the framebuffer
> - * on the first page. So we don't reserve this page for now because of
> - * that. Our current solution is to just prevent new nodes from being
> - * inserted on the first page - see the check we have at
> - * i915_gem_stolen_insert_node_in_range(). We may want to fix the fbcon
> - * problem later.
> - */
> + /* Basic memrange allocator for stolen space. */
> drm_mm_init(&dev_priv->mm.stolen, 0, ggtt->stolen_usable_size);
>
> + /* WaSkipStolenMemoryFirstPage:bdw+ */
> + if (INTEL_GEN(dev_priv) >= 8) {
> + dev_priv->mm.first_page.start = 0;
> + dev_priv->mm.first_page.size = 4096;
> + if (drm_mm_reserve_node(&dev_priv->mm.stolen,
> + &dev_priv->mm.first_page))
> + DRM_DEBUG_KMS("Failed to reserve the first page of
> stolen memory.\n");
> + }
If you are saying that the first page can never be used, then just don't
put into the range allocator.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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