Re: [PATCH v2 4/4] drm/i915: Codify our assumption that the Global GTT is <= 4GiB

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Mika Kuoppala <mika.kuoppala@linux.intel.com> writes:

> [ text/plain ]
> Joonas Lahtinen <joonas.lahtinen@linux.intel.com> writes:
>
>> [ text/plain ]
>> From: Chris Wilson <chris@chris-wilson.co.uk>
>>
>> Throughout the code base, we use u32 for offsets into the global GTT. If
>> we ever see any hardware with a larger GGTT, then we run the real risk
>> of silent corruption. So test for our assumption up front so that we
>> have a nice reminder should the time come when it fails.
>>
>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Cc: Daniel Vetter <daniel@ffwll.ch>
>> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
>> [Rebased and changed 1ull -> 1ULL]
>> ---
>>  drivers/gpu/drm/i915/i915_gem_gtt.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> index 8a9fa03..ba144ba 100644
>> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
>> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> @@ -3191,6 +3191,13 @@ int i915_gem_gtt_init(struct drm_device *dev)
>>  	if (ret)
>>  		return ret;
>>  
>> +	if ((ggtt->base.total - 1) >> 32) {
>> +		DRM_ERROR("We never expected a Global GTT with more than 32bits of address space! Found %lldM!\n",
>> +			  ggtt->base.total >> 20);
>> +		ggtt->base.total = 1ULL << 32;
>> +		ggtt->mappable_end = min(ggtt->mappable_end,
>> ggtt->base.total);
>
> mappable_end is not u64 so perhaps 
> s/min/min_t(u64,
>

Joonas pointed in irc that it is u64. Have been quite long already.
You can add my r-b without any change.

-Mika


> The mappable_end is really confusing after you realize it is used in 2
> different contexts where only in the other, it holds true. In the pa
> space, it definitely is not end but len. If we would rename it to
> mappable_len it would be ambivalent to context and more clear.
>
> With min_t change,
> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
>
>> +	}
>> +
>>  	/*
>>  	 * Initialise stolen early so that we may reserve preallocated
>>  	 * objects for the BIOS to KMS transition.
>> -- 
>> 2.5.0
>>
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