[Intel-gfx] [PATCH v2] drm/i915: limit PPGTT size to 2GB in 32-bit platforms

[Chris Wilson]

On Thu, May 28, 2015 at 06:09:34PM +0100, Michel Thierry wrote:
> And prevent overflow warning during compilation. We already set this limit
> for the GGTT.
> 
> This is a temporary patch until a full replacement of size_t variables
> (inadequate in 32-bit kernel) is in place.
> 
> Regression from:
> 	commit a4e0bedca678c81eea4cd79a4bd502335639f73a
> 	Author: Michel Thierry <michel.thierry at intel.com>
> 	Date:   Wed Apr 8 12:13:35 2015 +0100
> 
> 		drm/i915: Use complete address space in true PPGTT
> 
> v2: Prettify code and explain why this is needed. (Chris)
> 
> Suggested-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Michel Thierry <michel.thierry at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 17b7df0..0653c28 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -951,7 +951,16 @@ static int gen8_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
>  	gen8_initialize_pd(&ppgtt->base, ppgtt->scratch_pd);
>  
>  	ppgtt->base.start = 0;
> -	ppgtt->base.total = 1ULL << 32;

> +#ifdef CONFIG_X86_32
> +		/* While we have a proliferation of size_t variables
> +		 * we cannot represent the full ppgtt size on 32bit,
> +		 * so limit it to the same size as the GGTT (currently
> +		 * 2GiB).
> +		 */
> +		ppgtt->base.total = to_i915(ppgtt->base.dev)->gtt.base.total;
> +#else
> +		ppgtt->base.total = 1ULL << 32;
> +#endif

You missed the point of having it always compiled. Part of that is that
the compiler warning here is important.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre