Re: [Intel-gfx] [PATCH v3] drm/i915/mtl: Disable stolen memory backed FB for A0

["Das, Nirmoy" <nirmoy.das@linux.intel.com>]

On 4/4/2023 8:27 PM, Ville Syrjälä wrote:
> On Tue, Apr 04, 2023 at 08:13:42PM +0200, Nirmoy Das wrote:
>> Stolen memory is not usable for MTL A0 stepping beyond
>> certain access size and we have no control over userspace
>> access size of /dev/fb which can be backed by stolen memory.
>> So disable stolen memory backed fb by setting i915->dsm.usable_size
>> to zero.
>>
>> v2: remove hsdes reference and fix commit message(Andi)
>> v3: use revid as we want to target SOC stepping(Radhakrishna)
>>
>> Cc: Matthew Auld <matthew.auld@intel.com>
>> Cc: Andi Shyti <andi.shyti@linux.intel.com>
>> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
>> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
>> Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
>> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
>> Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
>> ---
>>   drivers/gpu/drm/i915/gem/i915_gem_stolen.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
>> index 8ac376c24aa2..ee492d823f1b 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
>> @@ -535,6 +535,14 @@ static int i915_gem_init_stolen(struct intel_memory_region *mem)
>>   	/* Basic memrange allocator for stolen space. */
>>   	drm_mm_init(&i915->mm.stolen, 0, i915->dsm.usable_size);
>>   
>> +	/*
>> +	 * Access to stolen lmem beyond certain size for MTL A0 stepping
>> +	 * would crash the machine. Disable stolen lmem for userspace access
>> +	 * by setting usable_size to zero.
>> +	 */
>> +	if (IS_METEORLAKE(i915) && INTEL_REVID(i915) == 0x0)
>> +		i915->dsm.usable_size = 0;
> That certainly won't prevent FBC from using stolen.
> Are we sure that FBC accesses are fine?

I think so. I remember Jouni tested this patch internally to unblock a 
FBC test.

Jouni, could you please share your thoughts. I can't seem to find the 
internal JIRA reference right now.


Regards,

Nirmoy

>
>> +
>>   	return 0;
>>   }
>>   
>> -- 
>> 2.39.0