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

[Sean V Kelley <sean.v.kelley@intel.com>]

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On Saturday 08 Mar 2014 at 09:25:54 (+0000), Chris Wilson writes :
> 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?

It should affect all baytrail systems. To my knowledge there are no subsets that have it fused off.

>  
> > Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> > Cc: Alan Cox <alan@linux.intel.com>
> > Cc: Fei Jiang <fei.jiang@intel.com>
> > Signed-off-by: Sean V Kelley <sean.v.kelley@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.

Thanks for the feedback also going through Daniel's.

Sean

> 
> >  	 */
> > -	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

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