Re: [PATCH v8 11/34] gpu: host1x: Add runtime PM and OPP support

[Ulf Hansson <ulf.hansson@xxxxxxxxxx>]

On Tue, 17 Aug 2021 at 16:03, Thierry Reding <thierry.reding@xxxxxxxxx> wrote:
>
> On Tue, Aug 17, 2021 at 02:04:38PM +0200, Ulf Hansson wrote:
> > On Tue, 17 Aug 2021 at 03:30, Dmitry Osipenko <digetx@xxxxxxxxx> wrote:
> > >
> > > Add runtime PM and OPP support to the Host1x driver. It's required for
> > > enabling system-wide DVFS and supporting dynamic power management using
> > > a generic power domain. For the starter we will keep host1x always-on
> > > because dynamic power management require a major refactoring of the driver
> > > code since lot's of code paths will need the RPM handling and we're going
> > > to remove some of these paths in the future. Host1x doesn't consume much
> > > power so it is good enough, we at least need to resume Host1x in order
> > > to initialize the power state.
> > >
> > > Tested-by: Peter Geis <pgwipeout@xxxxxxxxx> # Ouya T30
> > > Tested-by: Paul Fertser <fercerpav@xxxxxxxxx> # PAZ00 T20
> > > Tested-by: Nicolas Chauvet <kwizart@xxxxxxxxx> # PAZ00 T20 and TK1 T124
> > > Tested-by: Matt Merhar <mattmerhar@xxxxxxxxxxxxxx> # Ouya T30
> > > Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > > ---
> >
> > [...]
> >
> > > +
> > >  static int host1x_probe(struct platform_device *pdev)
> > >  {
> > >         struct host1x *host;
> > > @@ -394,6 +423,10 @@ static int host1x_probe(struct platform_device *pdev)
> > >         /* set common host1x device data */
> > >         platform_set_drvdata(pdev, host);
> > >
> > > +       err = devm_tegra_core_dev_init_opp_table_simple(&pdev->dev);
> > > +       if (err)
> > > +               return err;
> > > +
> > >         host->regs = devm_ioremap_resource(&pdev->dev, regs);
> > >         if (IS_ERR(host->regs))
> > >                 return PTR_ERR(host->regs);
> > > @@ -423,12 +456,9 @@ static int host1x_probe(struct platform_device *pdev)
> > >                 return err;
> > >         }
> > >
> > > -       host->rst = devm_reset_control_get(&pdev->dev, "host1x");
> > > -       if (IS_ERR(host->rst)) {
> > > -               err = PTR_ERR(host->rst);
> > > -               dev_err(&pdev->dev, "failed to get reset: %d\n", err);
> > > +       err = host1x_get_resets(host);
> > > +       if (err)
> > >                 return err;
> > > -       }
> > >
> > >         err = host1x_iommu_init(host);
> > >         if (err < 0) {
> > > @@ -443,22 +473,10 @@ static int host1x_probe(struct platform_device *pdev)
> > >                 goto iommu_exit;
> > >         }
> > >
> > > -       err = clk_prepare_enable(host->clk);
> > > -       if (err < 0) {
> > > -               dev_err(&pdev->dev, "failed to enable clock\n");
> > > -               goto free_channels;
> > > -       }
> > > -
> > > -       err = reset_control_deassert(host->rst);
> > > -       if (err < 0) {
> > > -               dev_err(&pdev->dev, "failed to deassert reset: %d\n", err);
> > > -               goto unprepare_disable;
> > > -       }
> > > -
> >
> > Removing the clk_prepare_enable() and reset_control_deassert() from
> > host1x_probe(), might not be a good idea. See more about why, below.
> >
> > >         err = host1x_syncpt_init(host);
> > >         if (err) {
> > >                 dev_err(&pdev->dev, "failed to initialize syncpts\n");
> > > -               goto reset_assert;
> > > +               goto free_channels;
> > >         }
> > >
> > >         err = host1x_intr_init(host, syncpt_irq);
> > > @@ -467,10 +485,14 @@ static int host1x_probe(struct platform_device *pdev)
> > >                 goto deinit_syncpt;
> > >         }
> > >
> > > -       host1x_debug_init(host);
> > > +       pm_runtime_enable(&pdev->dev);
> > >
> > > -       if (host->info->has_hypervisor)
> > > -               host1x_setup_sid_table(host);
> > > +       /* the driver's code isn't ready yet for the dynamic RPM */
> > > +       err = pm_runtime_resume_and_get(&pdev->dev);
> >
> > If the driver is being built with the CONFIG_PM Kconfig option being
> > unset, pm_runtime_resume_and_get() will return 0 to indicate success -
> > and without calling the ->runtime_resume() callback.
> > In other words, the clock will remain gated and the reset will not be
> > deasserted, likely causing the driver to be malfunctioning.
> >
> > If the driver isn't ever being built with CONFIG_PM unset, feel free
> > to ignore my above comments.
> >
> > Otherwise, if it needs to work both with and without CONFIG_PM being
> > set, you may use the following pattern in host1x_probe() to deploy
> > runtime PM support:
> >
> > "Enable the needed resources to probe the device"
> > pm_runtime_get_noresume()
> > pm_runtime_set_active()
> > pm_runtime_enable()
> >
> > "Before successfully completing probe"
> > pm_runtime_put()
>
> We made a conscious decision a few years ago to have ARCH_TEGRA select
> PM on both 32-bit and 64-bit ARM, specifically to avoid the need to do
> this dance (though there are still a few drivers left that do this, I
> think).
>
> So I think this should be unnecessary. Unless perhaps if the sysfs PM
> controls have any influence on this. As far as I know, as long as the
> PM kconfig option is enabled, the sysfs control only influence the
> runtime behaviour (i.e. setting the sysfs PM control to "on" is going
> to force runtime PM to be resumed) but there's no way to disable
> runtime PM altogether via sysfs that would make the above necessary.

Thanks for clarifying! As I said, feel free to ignore my comments then.

For this and the other patches in the series, I assume you only need
to care about whether the driver is a cross SoC driver and used on
other platforms than Tegra then.

>
> Thierry

Kind regards
Uffe