linux-kernel - Re: [PATCH v2] drm/nouveau/pmu: fix timeout on GP108

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Date:   Wed, 17 Feb 2021 12:30:30 +0900
From:   Alexandre Courbot <gnurou@...il.com>
To:     Diego Viola <diego.viola@...il.com>
Cc:     Ben Skeggs <bskeggs@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel@...ts.freedesktop.org, nouveau@...iet.org
Subject: Re: [PATCH v2] drm/nouveau/pmu: fix timeout on GP108

On Wed, Feb 17, 2021 at 1:20 AM Diego Viola <diego.viola@...il.com> wrote:
>
> This code times out on GP108, probably because the BIOS puts it into a
> bad state.
>
> Since we reset the PMU on driver load anyway, we are at no risk from
> missing a response from it since we are not waiting for one to begin
> with.

This looks safe to me, provided indeed that the PMU's reset is not
called outside of initialization (which for GP108 is shouldn't be
IIRC?).

>
> Signed-off-by: Diego Viola <diego.viola@...il.com>
> ---
>  drivers/gpu/drm/nouveau/nvkm/subdev/pmu/base.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/pmu/base.c b/drivers/gpu/drm/nouveau/nvkm/subdev/pmu/base.c
> index a0fe607c9c07..5c802f2d00cb 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/pmu/base.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/pmu/base.c
> @@ -102,12 +102,8 @@ nvkm_pmu_reset(struct nvkm_pmu *pmu)
>         if (!pmu->func->enabled(pmu))
>                 return 0;
>
> -       /* Inhibit interrupts, and wait for idle. */
> +       /* Inhibit interrupts. */
>         nvkm_wr32(device, 0x10a014, 0x0000ffff);
> -       nvkm_msec(device, 2000,
> -               if (!nvkm_rd32(device, 0x10a04c))
> -                       break;
> -       );
>
>         /* Reset. */
>         if (pmu->func->reset)
> --
> 2.30.1
>