linux-kernel - Re: [PATCH v4 5/7] drm/panfrost: Add support for multiple power domains

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Message-ID: <CAPDyKFrq5KQ7CHnMSCv7GqzpQyVfDQgLYjUVzeweTwKR3AmM4g@mail.gmail.com>
Date:   Mon, 10 Feb 2020 08:50:25 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Nicolas Boichat <drinkcat@...omium.org>
Cc:     Rob Herring <robh+dt@...nel.org>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Steven Price <steven.price@....com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>
Subject: Re: [PATCH v4 5/7] drm/panfrost: Add support for multiple power domains

On Sun, 9 Feb 2020 at 13:50, Nicolas Boichat <drinkcat@...omium.org> wrote:
>
> On Fri, Feb 7, 2020 at 10:26 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> >
> > On Fri, 7 Feb 2020 at 06:27, Nicolas Boichat <drinkcat@...omium.org> wrote:
> > >
> > > When there is a single power domain per device, the core will
> > > ensure the power domain is switched on (so it is technically
> > > equivalent to having not power domain specified at all).
> > >
> > > However, when there are multiple domains, as in MT8183 Bifrost
> > > GPU, we need to handle them in driver code.
> > >
> > > Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
> >
> > Besides a minor nitpick, feel free to add:
> >
> > Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>
> >
> > Kind regards
> > Uffe
> >
> > [snip]
> > > +static int panfrost_pm_domain_init(struct panfrost_device *pfdev)
> > > +{
> > > +       int err;
> > > +       int i, num_domains;
> > > +
> > > +       num_domains = of_count_phandle_with_args(pfdev->dev->of_node,
> > > +                                                "power-domains",
> > > +                                                "#power-domain-cells");
> > > +
> > > +       /*
> > > +        * Single domain is handled by the core, and, if only a single power
> > > +        * the power domain is requested, the property is optional.
> > > +        */
> > > +       if (num_domains < 2 && pfdev->comp->num_pm_domains < 2)
> > > +               return 0;
> > > +
> > > +       if (num_domains != pfdev->comp->num_pm_domains) {
> > > +               dev_err(pfdev->dev,
> > > +                       "Incorrect number of power domains: %d provided, %d needed\n",
> > > +                       num_domains, pfdev->comp->num_pm_domains);
> > > +               return -EINVAL;
> > > +       }
> > > +
> > > +       if (WARN(num_domains > ARRAY_SIZE(pfdev->pm_domain_devs),
> > > +                       "Too many supplies in compatible structure.\n"))
> >
> > Nitpick:
> > Not sure this deserves a WARN. Perhaps a regular dev_err() is sufficient.
>
> Ah well I had a BUG_ON before so presumably this is already a little better ,-)
>
> You can only reach there if you set pfdev->comp->num_pm_domains >
> MAX_PM_DOMAINS in the currently matched struct panfrost_compatible
> (pfdev->comp->num_pm_domains == num_domains, and see below too), so
> the kernel code would actually be actually broken (not the device
> tree, nor anything that could be probed). So I'm wondering if the
> loudness of a WARN is better in this case? Arguable ,-)

I see. It's not a big a deal, so feel free to keep as is.

[...]

Kind regards
Uffe