linux-kernel - Re: [PATCH v7 6/8] clk: tegra: cclk: Handle thermal DIV2 CPU frequency throttling

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Message-ID: <04bc9e16-be7e-cf18-9fff-436dd063bf10@gmail.com>
Date:   Tue, 11 May 2021 18:23:24 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, linux-tegra@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v7 6/8] clk: tegra: cclk: Handle thermal DIV2 CPU
 frequency throttling

11.05.2021 17:41, Michał Mirosław пишет:
> On Tue, May 11, 2021 at 02:17:35AM +0300, Dmitry Osipenko wrote:
>> Check whether thermal DIV2 throttle is active in order to report
>> the CPU frequency properly. This very useful for userspace tools
>> like cpufreq-info which show actual frequency asserted from hardware.
>>
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>  drivers/clk/tegra/clk-tegra-super-cclk.c | 16 ++++++++++++++--
>>  drivers/clk/tegra/clk-tegra30.c          |  2 +-
>>  2 files changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/clk/tegra/clk-tegra-super-cclk.c b/drivers/clk/tegra/clk-tegra-super-cclk.c
>> index a03119c30456..f75822b71d0e 100644
>> --- a/drivers/clk/tegra/clk-tegra-super-cclk.c
>> +++ b/drivers/clk/tegra/clk-tegra-super-cclk.c
>> @@ -25,6 +25,8 @@
>>  
>>  #define SUPER_CDIV_ENB		BIT(31)
>>  
>> +#define TSENSOR_SLOWDOWN	BIT(23)
>> +
>>  static struct tegra_clk_super_mux *cclk_super;
>>  static bool cclk_on_pllx;
>>  
>> @@ -47,10 +49,20 @@ static int cclk_super_set_rate(struct clk_hw *hw, unsigned long rate,
>>  static unsigned long cclk_super_recalc_rate(struct clk_hw *hw,
>>  					    unsigned long parent_rate)
>>  {
>> +	struct tegra_clk_super_mux *super = to_clk_super_mux(hw);
>> +	u32 val = readl_relaxed(super->reg);
>> +	unsigned int div2;
>> +
>> +	/* check whether thermal throttling is active */
>> +	if (val & TSENSOR_SLOWDOWN)
>> +		div2 = 2;
>> +	else
>> +		div2 = 1;
>> +
>>  	if (cclk_super_get_parent(hw) == PLLX_INDEX)
>> -		return parent_rate;
>> +		return parent_rate / div2;
>>  
>> -	return tegra_clk_super_ops.recalc_rate(hw, parent_rate);
>> +	return tegra_clk_super_ops.recalc_rate(hw, parent_rate) / div2;
>>  }
> 
> Could you check if the compiler can optimize out the division? I know this
> is a slow path, but nevertheless the 'shr' version would be the same amount
> of source code.

Hello Michał,

GCC can't optimize that division. I'll wait for more comments and then
update this patch in v8 with yours suggestion. Thank you for taking a
look at the patches.