On Mon, 26 Nov 2012 21:52:54 -0800
Ben Widawsky <ben at bwidawsk.net> wrote:
> This bug was introduced by me:
> commit e76e9aebcdbfebae8f4cd147e3c0f800d36e97f3
> Author: Ben Widawsky <ben at bwidawsk.net>
> Date: Sun Nov 4 09:21:27 2012 -0800
>
> drm/i915: Stop using AGP layer for GEN6+
>
> The existing code uses memset_io which follows memset semantics in only
> guaranteeing a write of individual bytes. Since a PTE entry is 4 bytes,
> this can only be correct if the scratch page address is 0.
>
> This caused unsightly errors when we clear the range at load time,
> though I'm not really sure what the heck is referencing that memory
> anyway. I caught this is because I believe we have some other bug where
> the display is doing reads of memory we feel should be cleared (or we
> are relying on scratch pages to be a specific value).
>
> Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
> ---
> drivers/gpu/drm/i915/i915_gem_gtt.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 51f79bb..f7ac61e 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -367,8 +367,9 @@ static void i915_ggtt_clear_range(struct drm_device *dev,
> {
> struct drm_i915_private *dev_priv = dev->dev_private;
> gtt_pte_t scratch_pte;
> - volatile void __iomem *gtt_base = dev_priv->mm.gtt->gtt + first_entry;
> + gtt_pte_t __iomem *gtt_base = dev_priv->mm.gtt->gtt + first_entry;
> const int max_entries = dev_priv->mm.gtt->gtt_total_entries - first_entry;
> + int i;
>
> if (INTEL_INFO(dev)->gen < 6) {
> intel_gtt_clear_range(first_entry, num_entries);
> @@ -381,7 +382,8 @@ static void i915_ggtt_clear_range(struct drm_device *dev,
> num_entries = max_entries;
>
> scratch_pte = pte_encode(dev, dev_priv->mm.gtt->scratch_page_dma, I915_CACHE_LLC);
> - memset_io(gtt_base, scratch_pte, num_entries * sizeof(scratch_pte));
> + for (i = 0; i < num_entries; i++)
> + iowrite32(scratch_pte, >t_base[i]);
> readl(gtt_base);
> }
>
"This has been slurped into -queued. Thanks for the patch" - or
something like that.
--
Ben Widawsky, Intel Open Source Technology Center
