[Nouveau] [RFC PATCH 03/29] subdev/volt/gk104: return error when read fails

[Karol Herbst]

On Sun, Oct 8, 2017 at 12:29 PM, Pierre Moreau <pierre.morrow at free.fr> wrote:
> On 2017-09-15 — 17:11, Karol Herbst wrote:
>> While my gpu was powered off, hwmon returned 0.6V as the current voltage.
>> If nvkm_rd32 fails for any reason, return the error.
>>
>> With that sensors will display a "N/A" instead of 0.6V.
>
> Small nitpick, add a comma between “that” and “sensors”.
> Otherwise,
>
> Reviewed-by: Pierre Moreau <pierre.morrow at free.fr>
>

I think in the end I am not _that_ happy with that change. nvkm_rd32
can't return an error code, but as we interpret the full register as
the value, values above 0x7fffffff are most likely an error on either
our side or the hardware side. When the GPU is suspended we get
0xffffffff out, but this code shouldn't be called in the first place
when the GPU is suspended. We can't really trust runpm as well due to
race conditions, waking up the GPU is another terrible idea.

>>
>> Signed-off-by: Karol Herbst <karolherbst at gmail.com>
>> ---
>>  drm/nouveau/nvkm/subdev/volt/gk104.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drm/nouveau/nvkm/subdev/volt/gk104.c b/drm/nouveau/nvkm/subdev/volt/gk104.c
>> index 1c744e02..53a7af9d 100644
>> --- a/drm/nouveau/nvkm/subdev/volt/gk104.c
>> +++ b/drm/nouveau/nvkm/subdev/volt/gk104.c
>> @@ -40,10 +40,15 @@ gk104_volt_get(struct nvkm_volt *base)
>>  {
>>       struct nvbios_volt *bios = &gk104_volt(base)->bios;
>>       struct nvkm_device *device = base->subdev.device;
>> -     u32 div, duty;
>> +     int div, duty;
>>
>>       div  = nvkm_rd32(device, 0x20340);
>> +     if (div < 0)
>> +             return div;
>> +
>>       duty = nvkm_rd32(device, 0x20344);
>> +     if (duty < 0)
>> +             return duty;
>>
>>       return bios->base + bios->pwm_range * duty / div;
>>  }
>> --
>> 2.14.1
>>
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