Nouveau - Apr 2014 - [PATCH 11/12] drm/nouveau: support GK20A in nouveau_accel_init()

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.
> +		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 (...) {
> +	/* 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.

Thierry
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On Tue, Mar 25, 2014 at 9:10 AM, Thierry Reding
<thierry.reding at gmail.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?
>
>> +             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.
>
>> +     /* 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.
>
> Thierry
>
> _______________________________________________
> dri-devel mailing list
> dri-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel
>

On Wed, Mar 26, 2014 at 1:27 PM, Ben Skeggs <skeggsb at gmail.com>
wrote:
> On Tue, Mar 25, 2014 at 9:10 AM, Thierry Reding
> <thierry.reding at gmail.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?

On Wed, Mar 26, 2014 at 1:27 PM, Ben Skeggs <skeggsb at gmail.com>
wrote:
> On Tue, Mar 25, 2014 at 9:10 AM, Thierry Reding
> <thierry.reding at gmail.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?