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

[Michel Thierry <michel.thierry@intel.com>]

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On 5/28/2015 10:14 PM, Chris Wilson wrote:
> 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@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@ffwll.ch>
>> Cc: Mika Kuoppala <mika.kuoppala@intel.com>
>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>> Signed-off-by: Michel Thierry <michel.thierry@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
I was under the impression that Daniel wanted to get rid of the warning 
too, that's why I didn't use IS_ENABLED().



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