linux-kernel - Re: [PATCH v4 3/5] soc/tegra: pmc: Ensure that clock rates aren't too high

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Date:   Thu, 25 Mar 2021 15:39:30 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Peter Geis <pgwipeout@...il.com>,
        Matt Merhar <mattmerhar@...tonmail.com>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/5] soc/tegra: pmc: Ensure that clock rates aren't
 too high

On Tue, Mar 02, 2021 at 03:25:00PM +0300, Dmitry Osipenko wrote:
> Switch all clocks of a power domain to a safe rate which is suitable
> for all possible voltages in order to ensure that hardware constraints
> aren't violated when power domain state toggles.
> 
> Tested-by: Peter Geis <pgwipeout@...il.com> # Ouya T30
> 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/soc/tegra/pmc.c | 92 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 90 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
> index f970b615ee27..a87645fac735 100644
> --- a/drivers/soc/tegra/pmc.c
> +++ b/drivers/soc/tegra/pmc.c
> @@ -237,6 +237,7 @@ struct tegra_powergate {
>  	unsigned int id;
>  	struct clk **clks;
>  	unsigned int num_clks;
> +	unsigned long *clk_rates;
>  	struct reset_control *reset;
>  };
>  
> @@ -641,6 +642,57 @@ static int __tegra_powergate_remove_clamping(struct tegra_pmc *pmc,
>  	return 0;
>  }
>  
> +static int tegra_powergate_prepare_clocks(struct tegra_powergate *pg)
> +{
> +	unsigned long safe_rate = 100 * 1000 * 1000;

This seems a bit arbitrary. Where did you come up with that value?

I'm going to apply this to see how it fares in our testing.

Thierry

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