linux-kernel - Re: [PATCH v12 3/4] drm/panfrost: devfreq: Disable devfreq when num

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Date:   Wed, 21 Apr 2021 12:00:24 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Rob Herring <robh@...nel.org>, Steven Price <steven.price@....com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
Cc:     Fei Shao <fshao@...omium.org>, Hsin-Yi Wang <hsinyi@...omium.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Kristian Kristensen <hoegsberg@...omium.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 3/4] drm/panfrost: devfreq: Disable devfreq when
 num_supplies > 1

Argh sorry I messed up the rebase and this doesn't even build...

I'll send v13.

On Wed, Apr 21, 2021 at 8:19 AM Nicolas Boichat <drinkcat@...omium.org> wrote:
>
> GPUs with more than a single regulator (e.g. G72 on MT8183) will
> require platform-specific handling for devfreq, for 2 reasons:
>  1. The opp core (drivers/opp/core.c:_generic_set_opp_regulator)
>     does not support multiple regulators, so we'll need custom
>     handlers.
>  2. Generally, platforms with 2 regulators have platform-specific
>     constraints on how the voltages should be set (e.g.
>     minimum/maximum voltage difference between them), so we
>     should not just create generic handlers that simply
>     change the voltages without taking care of those constraints.
>
> Disable devfreq for now on those GPUs.
>
> Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
> Reviewed-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> Reviewed-by: Steven Price <steven.price@....com>
> ---
>
> (no changes since v9)
>
> Changes in v9:
>  - Explain why devfreq needs to be disabled for GPUs with >1
>    regulators.
>
> Changes in v8:
>  - Use DRM_DEV_INFO instead of ERROR
>
> Changes in v7:
>  - Fix GPU ID in commit message
>
> Changes in v6:
>  - devfreq: New change
>
>  drivers/gpu/drm/panfrost/panfrost_devfreq.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> index 47d27e54a34f..aca3bb9a12e4 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
> @@ -92,9 +92,19 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
>         struct thermal_cooling_device *cooling;
>         struct panfrost_devfreq *pfdevfreq = &pfdev->pfdevfreq;
>
> -       ret = devm_pm_opp_set_regulators(dev, pfdev->comp->supply_names,
> -                                        pfdev->comp->num_supplies);
> -       if (ret) {
> +       if (pfdev->comp->num_supplies > 1) {
> +               /*
> +                * GPUs with more than 1 supply require platform-specific handling:
> +                * continue without devfreq
> +                */
> +               DRM_DEV_INFO(dev, "More than 1 supply is not supported yet\n");
> +               return 0;
> +       }
> +
> +       opp_table = dev_pm_opp_set_regulators(dev, pfdev->comp->supply_names,
> +                                             pfdev->comp->num_supplies);
> +       if (IS_ERR(opp_table)) {
> +               ret = PTR_ERR(opp_table);
>                 /* Continue if the optional regulator is missing */
>                 if (ret != -ENODEV) {
>                         DRM_DEV_ERROR(dev, "Couldn't set OPP regulators\n");
> --
> 2.31.1.368.gbe11c130af-goog
>