[Intel-gfx] [PATCH v2 2/4] drm/i915/gt: Ensure memory quiesced before invalidation

[Cavitt, Jonathan]

-----Original Message-----
From: Nirmoy Das <nirmoy.das at linux.intel.com> 
Sent: Wednesday, July 12, 2023 7:18 AM
To: Andi Shyti <andi.shyti at linux.intel.com>; Cavitt, Jonathan <jonathan.cavitt at intel.com>
Cc: Intel GFX <intel-gfx at lists.freedesktop.org>; Roper, Matthew D <matthew.d.roper at intel.com>; Chris Wilson <chris at chris-wilson.co.uk>; Mika Kuoppala <mika.kuoppala at linux.intel.com>
Subject: Re: [Intel-gfx] [PATCH v2 2/4] drm/i915/gt: Ensure memory quiesced before invalidation
>
>Hi Andi and Jonathan,
>
>On 6/27/2023 11:43 AM, Andi Shyti wrote:
>> From: Jonathan Cavitt <jonathan.cavitt at intel.com>
>>
>> All memory traffic must be quiesced before requesting
>> an aux invalidation on platforms that use Aux CCS.
>>
>> Fixes: 972282c4cf24 ("drm/i915/gen12: Add aux table invalidate for all engines")
>> Signed-off-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
>> Signed-off-by: Andi Shyti <andi.shyti at linux.intel.com>
>> Cc: <stable at vger.kernel.org> # v5.8+
>> ---
>>   drivers/gpu/drm/i915/gt/gen8_engine_cs.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/gen8_engine_cs.c b/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
>> index 563efee055602..e10e1ad0e841f 100644
>> --- a/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
>> +++ b/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
>> @@ -202,6 +202,13 @@ int gen12_emit_flush_rcs(struct i915_request *rq, u32 mode)
>>   {
>>   	struct intel_engine_cs *engine = rq->engine;
>>   
>> +	/*
>> +	 * Aux invalidations on Aux CCS platforms require
>> +	 * memory traffic is quiesced prior.
>
>I see that we are doing aux inval on EMIT_INVALIDATE so it make sense to
>
>  do if ((mode & EMIT_INVALIDATE) && !HAS_FLAT_CCS(engine->i915) )
>

This is agreeable, though I don't think there's any instances of us calling gen12_emit_flush_rcs with a blank mode,
since that wouldn't accomplish anything.  So I don't think the additional check/safety net is necessary, but it doesn't
hurt to have.

>> +	 */
>> +	if (!HAS_FLAT_CCS(engine->i915))
>> +		mode |= EMIT_FLUSH;
>
>I think this generic EMIT_FLUSH is not enough. I seeing some missing 
>flags for PIPE_CONTROL
>
>As per https://gfxspecs.intel.com/Predator/Home/Index/43904. It makes 
>sense to move this to a
>
>new function given the complexity of PIPE_CONTROL flags requires for this.
>

I'm assuming when you're talking about the missing flags for PIPE_CONTROL, you're
referring to CCS Flush, correct?  Because every other flag is already covered in the
EMIT_FLUSH path.

I feel like I had this conversation with Matt while the internal version was
developed back in February, and the consensus was that the CCS Flush
requirement was already covered.  On the other hand, it looks like the CCS Flush
requirement was only recently added back in May, so it might be worth
double-checking at the very least.

Although... if CCS Flush is a missing flag, I wonder how we're supposed to set it,
as there doesn’t appear to be a definition for such a flag in intel_gpu_commands.h...

-Jonathan Cavitt

>
>Regards,
>
>Nirmoy
>
>
>> +
>>   	if (mode & EMIT_FLUSH) {
>>   		u32 flags = 0;
>>   		int err;
>