Re: [Intel-gfx] [PATCH 02/22] drm/i915/gem: Specify address type for chained reloc batches

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 04/05/2020 12:53, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2020-05-04 12:49:03)
>>
>> On 04/05/2020 05:48, Chris Wilson wrote:
>>> It is required that a chained batch be in the same address domain as its
>>> parent, and also that must be specified in the command for earlier gen
>>> as it is not inferred from the chaining until gen6.
>>>
>>> Fixes: 964a9b0f611e ("drm/i915/gem: Use chained reloc batches")
>>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>>> ---
>>>    drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 12 ++++++------
>>>    1 file changed, 6 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
>>> index cce7df231cb9..ab0d4df13c0b 100644
>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
>>> @@ -1004,14 +1004,14 @@ static int reloc_gpu_chain(struct reloc_cache *cache)
>>>        GEM_BUG_ON(cache->rq_size + RELOC_TAIL > PAGE_SIZE  / sizeof(u32));
>>>        cmd = cache->rq_cmd + cache->rq_size;
>>>        *cmd++ = MI_ARB_CHECK;
>>> -     if (cache->gen >= 8) {
>>> +     if (cache->gen >= 8)
>>>                *cmd++ = MI_BATCH_BUFFER_START_GEN8;
>>> -             *cmd++ = lower_32_bits(batch->node.start);
>>> -             *cmd++ = upper_32_bits(batch->node.start);
>>> -     } else {
>>> +     else if (cache->gen >= 6)
>>>                *cmd++ = MI_BATCH_BUFFER_START;
>>> -             *cmd++ = lower_32_bits(batch->node.start);
>>> -     }
>>> +     else
>>> +             *cmd++ = MI_BATCH_BUFFER_START | MI_BATCH_GTT;
>>> +     *cmd++ = lower_32_bits(batch->node.start);
>>> +     *cmd++ = upper_32_bits(batch->node.start);
>>
>> MI_NOOP between batches on gen < 8 ?
> 
> batch->node.start is 32b on gen<8, so this is effectively a trailing NOOP
> after the BB_START. However, since it is after the 2 dword BB_START on
> earlier gen it is never even evaluated by the CS.

Right, okay, like I remembered how it worked from last week! :) Best to 
drop a comment still.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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