Re: [PATCH] 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 4:39 PM, Chris Wilson wrote:
> On Thu, May 28, 2015 at 04:24:47PM +0100, Michel Thierry wrote:
>> 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
>>
>> Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>> Cc: Mika Kuoppala <mika.kuoppala@intel.com>
>> Signed-off-by: Michel Thierry <michel.thierry@intel.com>
>> ---
>>   drivers/gpu/drm/i915/i915_gem_gtt.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> index 17b7df0..ffecb87 100644
>> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
>> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> @@ -951,7 +951,15 @@ static int gen8_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
>>   	gen8_initialize_pd(&ppgtt->base, ppgtt->scratch_pd);
>>   
>>   	ppgtt->base.start = 0;
>> +
>> +#ifdef CONFIG_X86_32
>> +	/* Limit 32b platforms to GGTT size (2GB) */
> Forgot the comment about why the limit is inplace and when it can be
> lifted. Remember comments are for *why* not *what*.
>
>> +	struct drm_i915_private *dev_priv = ppgtt->base.dev->dev_private;
> Fancy new fangled C.
>
>> +	ppgtt->base.total = dev_priv->gtt.base.total;
> 	ppgtt->base.total = to_i915(ppgtt->base.dev)->gtt.base.total;
>
>> +#else
>>   	ppgtt->base.total = 1ULL << 32;
>> +#endif
> Better yet would be:
> 	ppgtt->base.total = 1ULL << 32;
> 	if (IS_ENABLED(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;
> 	}
>
> However, I am afraid that it will become obsolete but be forgotten to be
> removed.
Yes, this is just for 4.2, Mika started working on a patch to replace 
the size_t variables.
I'll update this with your changes.

Thanks,

> -Chris
>

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