[Intel-gfx] [PATCH] drm/i915: Allow null render state batchbuffers bigger than one page

[Chris Wilson]

Quoting Oscar Mateo (2017-07-14 15:52:59)
> 
> 
> 
> On 07/13/2017 03:28 PM, Rodrigo Vivi wrote:
> > On Wed, May 3, 2017 at 9:31 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> >> On Wed, May 03, 2017 at 09:12:18AM +0000, Oscar Mateo wrote:
> >>>     On 05/03/2017 08:52 AM, Mika Kuoppala wrote:
> >>>
> >>>   Oscar Mateo [1]<oscar.mateo at intel.com> writes:
> >>>
> >>>
> >>>   On 05/02/2017 09:17 AM, Mika Kuoppala wrote:
> >>>
> >>>   Chris Wilson [2]<chris at chris-wilson.co.uk> writes:
> >>>
> >>>
> >>>   On Fri, Apr 28, 2017 at 09:11:06AM +0000, Oscar Mateo wrote:
> >>>
> >>>   The new batchbuffer for CNL surpasses the 4096 byte mark.
> >>>
> >>>   Cc: Mika Kuoppala [3]<mika.kuoppala at intel.com>
> >>>   Cc: Ben Widawsky [4]<ben at bwidawsk.net>
> >>>   Signed-off-by: Oscar Mateo [5]<oscar.mateo at intel.com>
> >>>
> >>>   Evil, 4k+ of nothing-ness that userspace then has to configure for itself
> >>>   for correctness anyway.
> >>>
> >>>   Patch looks ok, but still question the sanity.
> >>>
> >>>   Is there a requirement for CNL to init the renderstate?
> >>>
> >>>   I would like to drop the render state init from CNL if
> >>>   we can't find evidence that it needs it. Bspec indicates
> >>>   that it doesnt.
> > I'd like to drop as well, and I was hearing people around telling we
> > didn't need anymore,
> > however without this during power on I had bad failures...
> >
> 
> The best I could get from architecture (+Raf) is that setting valid and 
> coherent values for the whole render state is required as soon as the 
> context is created, no matter who does it. If you see failures when the 
> KMD does not do it, that means the UMD must be missing something, right?

That is my initial response as well. The kernel does load one context,
just so that the hardware always has space to write to on power saving.
The only batch executed for it is the golden render state. Easy enough
to only initialise that kernel context to isolate whether it is
self-inflicted or that userspace overlooked something in its state
management. (I have the view that even if userspace doesn't think it
needs to use a particular bit of state today, tomorrow it will so will
need it anyway!)
-Chris
>