Re: [PATCH 1/3] drm/i915: Enable resource streamer bits on MI_BATCH_BUFFER_START

[Dave Gordon <david.s.gordon@intel.com>]

On 08/06/15 18:42, Abdiel Janulgue wrote:
> 
> On 06/08/2015 07:10 PM, Ville Syrjälä wrote:
>> On Mon, Jun 08, 2015 at 01:04:07PM +0300, Abdiel Janulgue wrote:
>>> Adds support for executing the resource streamer on BDW and HSW
>>>
>>> v2: Add support for Execlists (Minu Mathai <minu.mathai@intel.com>)
>>>
>>> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
>>> Signed-off-by: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
>>> ---
>>>  drivers/gpu/drm/i915/i915_reg.h         | 1 +
>>>  drivers/gpu/drm/i915/intel_lrc.c        | 4 +++-
>>>  drivers/gpu/drm/i915/intel_ringbuffer.c | 8 ++++++--
>>>  drivers/gpu/drm/i915/intel_ringbuffer.h | 1 +
>>>  4 files changed, 11 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
>>> index b522eb6..238bb25 100644
>>> --- a/drivers/gpu/drm/i915/i915_reg.h
>>> +++ b/drivers/gpu/drm/i915/i915_reg.h
>>> @@ -356,6 +356,7 @@
>>>  #define MI_BATCH_BUFFER_START	MI_INSTR(0x31, 0)
>>>  #define   MI_BATCH_GTT		    (2<<6) /* aliased with (1<<7) on gen4 */
>>>  #define MI_BATCH_BUFFER_START_GEN8	MI_INSTR(0x31, 1)
>>> +#define   MI_BATCH_RESOURCE_STREAMER (1<<10)
>>>  
>>>  #define MI_PREDICATE_SRC0	(0x2400)
>>>  #define MI_PREDICATE_SRC1	(0x2408)
>>> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
>>> index fcb074b..3b168f6 100644
>>> --- a/drivers/gpu/drm/i915/intel_lrc.c
>>> +++ b/drivers/gpu/drm/i915/intel_lrc.c
>>> @@ -1172,7 +1172,9 @@ static int gen8_emit_bb_start(struct intel_ringbuffer *ringbuf,
>>>  		return ret;
>>>  
>>>  	/* FIXME(BDW): Address space and security selectors. */
>>> -	intel_logical_ring_emit(ringbuf, MI_BATCH_BUFFER_START_GEN8 | (ppgtt<<8));
>>> +	intel_logical_ring_emit(ringbuf, MI_BATCH_BUFFER_START_GEN8 |
>>> +				(ppgtt<<8) | (I915_DISPATCH_RS ?
>>
>> That doesn't look right.
> 
> Yay.. Didn't catch these since this path never gets executed under GEN8
> anyway which uses execlist not legacy batch buffer execution. Better
> remove this then.

But GEN8 HW can run in legacy ringbuffer mode, and the driver continues
to support it, at least for now, so AFAIK there's nothing preventing you
using the Resource Streamer in ringbuffer mode; indeed I note that the
MI_RS_CONTEXT instruction can ONLY be used in ringbuffer mode.

Please don't conflate changes that are (or ought to be) orthogonal, such
as 32- vs 48-bit addressing and ringbuffer vs. execlists, just because
they were introduced in the same h/w generation ...

.Dave.
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