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

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Oscar Mateo <oscar.mateo@intel.com> writes:

> On 05/02/2017 09:17 AM, Mika Kuoppala wrote:
>> Chris Wilson <chris@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 <mika.kuoppala@intel.com>
>>>> Cc: Ben Widawsky <ben@bwidawsk.net>
>>>> Signed-off-by: Oscar Mateo <oscar.mateo@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.
>>
>> -Mika
>
> Hi Mika,
>
> I can double-check with the hardware architects, but word around here is 
> that render state init has never stopped being a requirement. Where did 
> you see in the BSpec that it is not required for CNL?
>

It would be great if you could refresh the answer and perhaps
even get some answers to the 'why' parts.

In the "Context Descriptor Format" section, it says:
"Render CS Only: Render state need not be initialized; the Render
Context Restore Inhibit bit in the Context/Save image in memory should
be set to prevent restoring garbage render context."

-Mika
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