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

[Dmitry Osipenko]

01.10.2021 16:27, Ulf Hansson пишет:
> On Mon, 27 Sept 2021 at 00:42, Dmitry Osipenko <digetx@xxxxxxxxx> 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@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>
>> ---
>>  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?

I'll keep it open-coded for now. This code is specific to Tegra because
normally ceil error shouldn't fall back to the floor, but for Tegra it's
expected to happen and it's a normal condition.