Re: [PATCH v1 2/2] cpufreq: tegra20: Use PLL_C as intermediate clock source

[Peter De Schrijver]

On Wed, May 23, 2018 at 07:00:20PM +0300, Dmitry Osipenko wrote:
> PLL_C is running at 600MHz which is significantly higher than the 216MHz
> of the PLL_P and it is known that PLL_C is always-ON because AHB BUS is
> running on that PLL. Let's use PLL_C as intermediate clock source, making
> CPU snappier a tad during of the frequency transition.
> 

pll_c isn't necessarily 600Mhz when used as a source for the second display
head.

Peter.

> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> ---
>  drivers/cpufreq/tegra20-cpufreq.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cpufreq/tegra20-cpufreq.c b/drivers/cpufreq/tegra20-cpufreq.c
> index 3ad6bded6efc..4bf5ba7da40b 100644
> --- a/drivers/cpufreq/tegra20-cpufreq.c
> +++ b/drivers/cpufreq/tegra20-cpufreq.c
> @@ -25,12 +25,13 @@
>  #include <linux/types.h>
>  
>  #define PLL_P_FREQ	216000
> +#define PLL_C_FREQ	600000
>  
>  static struct cpufreq_frequency_table freq_table[] = {
>  	{ .frequency = 216000 },
>  	{ .frequency = 312000 },
>  	{ .frequency = 456000 },
> -	{ .frequency = 608000 },
> +	{ .frequency = 600000 },
>  	{ .frequency = 760000 },
>  	{ .frequency = 816000 },
>  	{ .frequency = 912000 },
> @@ -44,6 +45,7 @@ struct tegra20_cpufreq {
>  	struct clk *cpu_clk;
>  	struct clk *pll_x_clk;
>  	struct clk *pll_p_clk;
> +	struct clk *pll_c_clk;
>  	bool pll_x_prepared;
>  };
>  
> @@ -58,7 +60,10 @@ static unsigned int tegra_get_intermediate(struct cpufreq_policy *policy,
>  	if (index == 0 || policy->cur == PLL_P_FREQ)
>  		return 0;
>  
> -	return PLL_P_FREQ;
> +	if (index == 3 || policy->cur == PLL_C_FREQ)
> +		return 0;
> +
> +	return PLL_C_FREQ;
>  }
>  
>  static int tegra_target_intermediate(struct cpufreq_policy *policy,
> @@ -79,7 +84,7 @@ static int tegra_target_intermediate(struct cpufreq_policy *policy,
>  	 */
>  	clk_prepare_enable(cpufreq->pll_x_clk);
>  
> -	ret = clk_set_parent(cpufreq->cpu_clk, cpufreq->pll_p_clk);
> +	ret = clk_set_parent(cpufreq->cpu_clk, cpufreq->pll_c_clk);
>  	if (ret)
>  		clk_disable_unprepare(cpufreq->pll_x_clk);
>  	else
> @@ -101,6 +106,9 @@ static int tegra_target(struct cpufreq_policy *policy, unsigned int index)
>  	if (index == 0)
>  		return clk_set_parent(cpufreq->cpu_clk, cpufreq->pll_p_clk);
>  
> +	if (index == 3)
> +		return clk_set_parent(cpufreq->cpu_clk, cpufreq->pll_c_clk);
> +
>  	ret = clk_set_rate(cpufreq->pll_x_clk, rate * 1000);
>  	/* Restore to earlier frequency on error, i.e. pll_x */
>  	if (ret)
> @@ -174,6 +182,12 @@ static int tegra20_cpufreq_probe(struct platform_device *pdev)
>  		goto put_pll_x;
>  	}
>  
> +	cpufreq->pll_c_clk = clk_get_sys(NULL, "pll_c");
> +	if (IS_ERR(cpufreq->pll_c_clk)) {
> +		err = PTR_ERR(cpufreq->pll_c_clk);
> +		goto put_pll_p;
> +	}
> +
>  	cpufreq->dev = &pdev->dev;
>  	cpufreq->driver.get = cpufreq_generic_get;
>  	cpufreq->driver.attr = cpufreq_generic_attr;
> @@ -190,12 +204,14 @@ static int tegra20_cpufreq_probe(struct platform_device *pdev)
>  
>  	err = cpufreq_register_driver(&cpufreq->driver);
>  	if (err)
> -		goto put_pll_p;
> +		goto put_pll_c;
>  
>  	platform_set_drvdata(pdev, cpufreq);
>  
>  	return 0;
>  
> +put_pll_c:
> +	clk_put(cpufreq->pll_c_clk);
>  put_pll_p:
>  	clk_put(cpufreq->pll_p_clk);
>  put_pll_x:
> @@ -212,6 +228,7 @@ static int tegra20_cpufreq_remove(struct platform_device *pdev)
>  
>  	cpufreq_unregister_driver(&cpufreq->driver);
>  
> +	clk_put(cpufreq->pll_c_clk);
>  	clk_put(cpufreq->pll_p_clk);
>  	clk_put(cpufreq->pll_x_clk);
>  	clk_put(cpufreq->cpu_clk);
> -- 
> 2.17.0
>