[Intel-gfx] [PATCH] drm/i915/icl: Adjust BSD2 semantics to mean any second VCS instance

[Tvrtko Ursulin]

On 20/04/2018 15:19, Bloomfield, Jon wrote:
>> -----Original Message-----
>> From: Tvrtko Ursulin <tursulin at ursulin.net>
>> Sent: Wednesday, April 18, 2018 2:34 AM
>> To: Intel-gfx at lists.freedesktop.org
>> Cc: tursulin at ursulin.net; Ursulin, Tvrtko <tvrtko.ursulin at intel.com>; Chris
>> Wilson <chris at chris-wilson.co.uk>; Bloomfield, Jon
>> <jon.bloomfield at intel.com>; Ye, Tony <tony.ye at intel.com>
>> Subject: [PATCH] drm/i915/icl: Adjust BSD2 semantics to mean any second
>> VCS instance
>>
>> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>
>> Currently our driver assumes BSD2 means hardware engine instance number
>> two. This does not work for Icelake parts with two VCS engines, but which
>> are hardware instances 0 and 2, and not 0 and 1 as with previous parts.
>>
>> This makes the second engine not discoverable via HAS_BSD2 get param, nor
>> it can be targetted by execbuf.
>>
>> While we are working on the next generation execbuf put in a hack which
>> allows discovery and access to this second VCS engine using legacy ABI.
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>> Cc: Jon Bloomfield <jon.bloomfield at intel.com>
>> Cc: Tony Ye <tony.ye at intel.com>
> I would advocate this patch being merged while the new execbuf API is being
> developed. Currently there is no way to submit to 2 engine skus with non-sequential
> engine id's. This doesn't introduce a new ABI, and there is no reason that I can see
> that the new execbuf solution couldn't be made backward compatible with this.

It is a bit of a awkward period to commit to this permanently because it 
only solves a subset of problem space and that makes it a hard sell in 
that context.

If there was legacy userspace which ran on 2 VCS Gen11 then maybe, but 
otherwise I think best is just wait for the new execbuf API. Or in fact 
would there be _any_ upstream userspace using this before the new 
execbuf API happens?

Regards,

Tvrtko