Re: [Intel-gfx] [PATCH] drm/i915/selftests: add prefetch padding to store_dw batchbuffer

[Matthew Auld <matthew.auld@intel.com>]

On 19/10/2022 10:12, Matthew Auld wrote:
> On 19/10/2022 08:12, Andrzej Hajda wrote:
>> Instruction prefetch mechanism requires that 512 bytes after the last
>> command should be readable by EU. Otherwise DMAR errors and engine
>> hangs can happen.
>>
>> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5278
>> Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
> 
> Is there a Bspec ref for this? I would have assumed that EU was more 
> about kernels/shaders, than simple MI commands? Also should we be 
> hitting dmar errors for ppGTT if this were some kind of overfetch? 
> AFAICT we always point entries back to scratch, unlike with say the GGTT 
> where we might have stale entries, and unbinding should flush the tlb?

s/unbinding/put_pages/

> 
>> ---
>>   drivers/gpu/drm/i915/gem/selftests/igt_gem_utils.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gem/selftests/igt_gem_utils.c 
>> b/drivers/gpu/drm/i915/gem/selftests/igt_gem_utils.c
>> index 3c55e77b0f1b00..fe999a02f8e10a 100644
>> --- a/drivers/gpu/drm/i915/gem/selftests/igt_gem_utils.c
>> +++ b/drivers/gpu/drm/i915/gem/selftests/igt_gem_utils.c
>> @@ -50,7 +50,7 @@ igt_emit_store_dw(struct i915_vma *vma,
>>       u32 *cmd;
>>       int err;
>> -    size = (4 * count + 1) * sizeof(u32);
>> +    size = (4 * count + 1) * sizeof(u32) + 512;
>>       size = round_up(size, PAGE_SIZE);
>>       obj = i915_gem_object_create_internal(vma->vm->i915, size);
>>       if (IS_ERR(obj))