[Intel-gfx] [PATCH] drm/i915: fix vxd392 memory corruption on VLV and >4GB

[Chris Wilson]

On Fri, Mar 07, 2014 at 05:13:51PM -0800, Sean V Kelley wrote:
> On VLV systems addressing 4GB of memory or greater, memory corruption was seen
> when initializing and attempting to render VP8 hardware decode surfaces using
> the VXD392 HW IP block.
> 
> The VXD MMU has a limitation to addressing only 32bits.  On 64bit kernel and
> user space builds this can cause problems for use of that IP block.
> 
> When 2G memory is inserted, fw buffer pfn was at 0x5f62b, which is below 4GB.
> While for 4GB of memory the fw buffer pfn was 0x162ea9 with a physical address
> at 0x162ea9000, above 4GB.
> 
> So although the memory is 4GB in the test hardware (Bayleybay CRB), a large
> physical region (for example 3G-4G) can be occupied by onboard system
> resources.
> 
> Enabling ZONE_DMA32 and setting the correct mask DMA for this device
> resolves the issue kernel side.

That's a shame. I guess this is restricted to a subset of byt?
 
> Cc: Jesse Barnes <jbarnes at virtuousgeek.org>
> Cc: Alan Cox <alan at linux.intel.com>
> Cc: Fei Jiang <fei.jiang at intel.com>
> Signed-off-by: Sean V Kelley <sean.v.kelley at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_dma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
> index e4d2b9f..b8c6efc 100644
> --- a/drivers/gpu/drm/i915/i915_dma.c
> +++ b/drivers/gpu/drm/i915/i915_dma.c
> @@ -1636,7 +1636,7 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
>  	 * behaviour if any general state is accessed within a page above 4GB,
>  	 * which also needs to be handled carefully.

Also add a sentence here giving a quick explanation as to why we need to
quirk IS_VLV as well.

>  	 */
> -	if (IS_BROADWATER(dev) || IS_CRESTLINE(dev))
> +	if (IS_BROADWATER(dev) || IS_CRESTLINE(dev) || IS_VALLEYVIEW(dev))
>  		dma_set_coherent_mask(&dev->pdev->dev, DMA_BIT_MASK(32));
>  
>  	aperture_size = dev_priv->gtt.mappable_end;

-- 
Chris Wilson, Intel Open Source Technology Centre