linux-kernel - Re: [PATCH 11/12] drm/nouveau: support GK20A in nouveau_accel

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Date:	Wed, 2 Apr 2014 23:14:10 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Ben Skeggs <skeggsb@...il.com>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <acourbot@...dia.com>,
	"nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Ben Skeggs <bskeggs@...hat.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 11/12] drm/nouveau: support GK20A in nouveau_accel_init()

On Wed, Mar 26, 2014 at 1:27 PM, Ben Skeggs <skeggsb@...il.com> wrote:
> On Tue, Mar 25, 2014 at 9:10 AM, Thierry Reding
> <thierry.reding@...il.com> wrote:
>> On Mon, Mar 24, 2014 at 05:42:33PM +0900, Alexandre Courbot wrote:
>>> GK20A does not embed a dedicated COPY engine and thus cannot allocate
>>> the copy channel that nouveau_accel_init() attempts to create. It also
>>> lacks any display hardware, so the creation of a software channel does
>>> not apply neither.
>>
>> Perhaps this should be two separate patches?
>>
>>> diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
>> [...]
>>> +     if (device->chipset == 0xea) {
>>> +             /* gk20a does not have CE0/CE1 */
>>
>> This would be another good candidate for a feature flag.
> There are ways to query this in a chipset-independent way.  However,
> despite reporting it as an error if no copy engines are available, the
> code should continue on without the channel happily.  Perhaps we can
> just punt the relevent error messages to a debug loglevel for now?

Sure, that would be more future-proof as well.

>
>>
>>> +             arg0 = NVE0_CHANNEL_IND_ENGINE_GR;
>>> +             arg1 = 1;
>>> +     } else
>>>       if (device->card_type >= NV_E0) {
>>
>> The formatting here is somewhat weird. From a brief look I couldn't find
>> any indication that nouveau deviates from the standard coding style, so
>> this should be:
>>
>>         } else if (...) {
> I use the former in a few places, despite it not entirely being
> "correct".. It looks nicer though :)  I don't mind either way though.

Yeah, I just followed the style of the file here. Whether it needs to
change or not is not my call. :P

>>> +     /* Need to figure out how to handle sw for gk20a */
>>> +     if (device->chipset == 0xea)
>>> +             goto skip_sw_init;
>>
>> The commit message makes it sound like SW isn't needed since gk20a
>> "lacks any display hardware". In that case the comment here doesn't make
>> much sense.

Correct. As far as I have looked (that is, not very far), SW methods
are used for display-related functions, but there might be other
use-cases too. Maybe someone who knows better can confirm?
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