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

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Message-ID: <CAAVeFu+zySrMNUjzZ7qrB-MdqHvrGMg2WD5YmHzZ7yA5dFqyrA@mail.gmail.com>
Date:	Wed, 16 Apr 2014 14:57:40 +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?

Do you know how to query this in a chipset-independant way? I have
failed to find any information for this.

The code does continue without any issue after reporting the error, so
indeed that check is not strictly necessary. But I was just mimicking
what follows right after:

    if (device->chipset >= 0xa3 &&
        device->chipset != 0xaa &&
        device->chipset != 0xac) {
        ret = nouveau_channel_new(drm, &drm->client, NVDRM_DEVICE,
                      NVDRM_CHAN + 1, NvDmaFB, NvDmaTT,
                      &drm->cechan);
        if (ret)
            NV_ERROR(drm, "failed to create ce channel, %d\n", ret);

        arg0 = NvDmaFB;
        arg1 = NvDmaTT;
    } else {
        arg0 = NvDmaFB;
        arg1 = NvDmaTT;
    }

So if we are trying to avoid showing this error for 0xa0 class
devices, why not for NV_E0?
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