linux-kernel - Re: [PATCH v13 11/35] drm/tegra: dc: Support OPP and SoC core voltage scaling

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Date:   Fri, 1 Oct 2021 15:27:20 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>,
        Viresh Kumar <vireshk@...nel.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Peter Chen <peter.chen@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Nishanth Menon <nm@...com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Michael Turquette <mturquette@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        linux-staging@...ts.linux.dev, linux-pwm@...r.kernel.org,
        linux-mmc <linux-mmc@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Lucas Stach <dev@...xeye.de>, Stefan Agner <stefan@...er.ch>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        David Heidelberg <david@...t.cz>
Subject: Re: [PATCH v13 11/35] drm/tegra: dc: Support OPP and SoC core voltage scaling

On Mon, 27 Sept 2021 at 00:42, Dmitry Osipenko <digetx@...il.com> wrote:
>
> Add OPP and SoC core voltage scaling support to the display controller
> driver. This is required for enabling system-wide DVFS on pre-Tegra186
> SoCs.
>
> Tested-by: Peter Geis <pgwipeout@...il.com> # Ouya T30
> Tested-by: Paul Fertser <fercerpav@...il.com> # PAZ00 T20
> Tested-by: Nicolas Chauvet <kwizart@...il.com> # PAZ00 T20 and TK1 T124
> Tested-by: Matt Merhar <mattmerhar@...tonmail.com> # Ouya T30
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/gpu/drm/tegra/dc.c | 74 ++++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/tegra/dc.h |  2 ++
>  2 files changed, 76 insertions(+)
>
> diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
> index a29d64f87563..d4047a14e2b6 100644
> --- a/drivers/gpu/drm/tegra/dc.c
> +++ b/drivers/gpu/drm/tegra/dc.c
> @@ -11,9 +11,12 @@
>  #include <linux/interconnect.h>
>  #include <linux/module.h>
>  #include <linux/of_device.h>
> +#include <linux/pm_domain.h>
> +#include <linux/pm_opp.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/reset.h>
>
> +#include <soc/tegra/common.h>
>  #include <soc/tegra/pmc.h>
>
>  #include <drm/drm_atomic.h>
> @@ -1762,6 +1765,47 @@ int tegra_dc_state_setup_clock(struct tegra_dc *dc,
>         return 0;
>  }
>
> +static void tegra_dc_update_voltage_state(struct tegra_dc *dc,
> +                                         struct tegra_dc_state *state)
> +{
> +       unsigned long rate, pstate;
> +       struct dev_pm_opp *opp;
> +       int err;
> +
> +       if (!dc->has_opp_table)
> +               return;
> +
> +       /* calculate actual pixel clock rate which depends on internal divider */
> +       rate = DIV_ROUND_UP(clk_get_rate(dc->clk) * 2, state->div + 2);
> +
> +       /* find suitable OPP for the rate */
> +       opp = dev_pm_opp_find_freq_ceil(dc->dev, &rate);
> +
> +       if (opp == ERR_PTR(-ERANGE))
> +               opp = dev_pm_opp_find_freq_floor(dc->dev, &rate);
> +
> +       if (IS_ERR(opp)) {
> +               dev_err(dc->dev, "failed to find OPP for %luHz: %pe\n",
> +                       rate, opp);
> +               return;
> +       }
> +
> +       pstate = dev_pm_opp_get_required_pstate(opp, 0);
> +       dev_pm_opp_put(opp);
> +
> +       /*
> +        * The minimum core voltage depends on the pixel clock rate (which
> +        * depends on internal clock divider of the CRTC) and not on the
> +        * rate of the display controller clock. This is why we're not using
> +        * dev_pm_opp_set_rate() API and instead controlling the power domain
> +        * directly.
> +        */
> +       err = dev_pm_genpd_set_performance_state(dc->dev, pstate);
> +       if (err)
> +               dev_err(dc->dev, "failed to set power domain state to %lu: %d\n",
> +                       pstate, err);

Yeah, the above code looks very similar to the code I pointed to in
patch6. Perhaps we need to discuss with Viresh, whether it makes sense
to fold in a patch adding an opp helper function after all, to avoid
the open coding.

Viresh?

[...]

Kind regards
Uffe