Re: [PATCH mvebu v3 02/10] cpufreq: armada-37xx: Fix setting TBG parent for load levels

[Gregory CLEMENT <gregory.clement@bootlin.com>]

Pali Rohár <pali@kernel.org> writes:

> From: Marek Behún <kabel@kernel.org>
>
> With CPU frequency determining software [1] we have discovered that
> after this driver does one CPU frequency change, the base frequency of
> the CPU is set to the frequency of TBG-A-P clock, instead of the TBG
> that is parent to the CPU.
>
> This can be reproduced on EspressoBIN and Turris MOX:
>   cd /sys/devices/system/cpu/cpufreq/policy0
>   echo powersave >scaling_governor
>   echo performance >scaling_governor
>
> Running the mhz tool before this driver is loaded reports 1000 MHz, and
> after loading the driver and executing commands above the tool reports
> 800 MHz.
>
> The change of TBG clock selector is supposed to happen in function
> armada37xx_cpufreq_dvfs_setup. Before the function returns, it does
> this:
>   parent = clk_get_parent(clk);
>   clk_set_parent(clk, parent);
>
> The armada-37xx-periph clock driver has the .set_parent method
> implemented correctly for this, so if the method was actually called,
> this would work. But since the introduction of the common clock
> framework in commit b2476490ef11 ("clk: introduce the common clock..."),
> the clk_set_parent function checks whether the parent is actually
> changing, and if the requested new parent is same as the old parent
> (which is obviously the case for the code above), the .set_parent method
> is not called at all.
>
> This patch fixes this issue by filling the correct TBG clock selector
> directly in the armada37xx_cpufreq_dvfs_setup during the filling of
> other registers at the same address. But the determination of CPU TBG
> index cannot be done via the common clock framework, therefore we need
> to access the North Bridge Peripheral Clock registers directly in this
> driver.
>
> [1] https://github.com/wtarreau/mhz
>
> Signed-off-by: Marek Behún <kabel@kernel.org>
> Tested-by: Pali Rohár <pali@kernel.org>
> Tested-by: Tomasz Maciej Nowak <tmn505@gmail.com>
> Tested-by: Anders Trier Olesen <anders.trier.olesen@gmail.com>
> Tested-by: Philip Soares <philips@netisense.com>
> Fixes: 92ce45fb875d ("cpufreq: Add DVFS support for Armada 37xx")
> Cc: stable@vger.kernel.org

Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>

Thanks,

Gregory
> ---
>  drivers/cpufreq/armada-37xx-cpufreq.c | 35 ++++++++++++++++++---------
>  1 file changed, 23 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/cpufreq/armada-37xx-cpufreq.c b/drivers/cpufreq/armada-37xx-cpufreq.c
> index b4af4094309b..b8dc6c849579 100644
> --- a/drivers/cpufreq/armada-37xx-cpufreq.c
> +++ b/drivers/cpufreq/armada-37xx-cpufreq.c
> @@ -25,6 +25,10 @@
>  
>  #include "cpufreq-dt.h"
>  
> +/* Clk register set */
> +#define ARMADA_37XX_CLK_TBG_SEL		0
> +#define ARMADA_37XX_CLK_TBG_SEL_CPU_OFF	22
> +
>  /* Power management in North Bridge register set */
>  #define ARMADA_37XX_NB_L0L1	0x18
>  #define ARMADA_37XX_NB_L2L3	0x1C
> @@ -120,10 +124,15 @@ static struct armada_37xx_dvfs *armada_37xx_cpu_freq_info_get(u32 freq)
>   * will be configured then the DVFS will be enabled.
>   */
>  static void __init armada37xx_cpufreq_dvfs_setup(struct regmap *base,
> -						 struct clk *clk, u8 *divider)
> +						 struct regmap *clk_base, u8 *divider)
>  {
> +	u32 cpu_tbg_sel;
>  	int load_lvl;
> -	struct clk *parent;
> +
> +	/* Determine to which TBG clock is CPU connected */
> +	regmap_read(clk_base, ARMADA_37XX_CLK_TBG_SEL, &cpu_tbg_sel);
> +	cpu_tbg_sel >>= ARMADA_37XX_CLK_TBG_SEL_CPU_OFF;
> +	cpu_tbg_sel &= ARMADA_37XX_NB_TBG_SEL_MASK;
>  
>  	for (load_lvl = 0; load_lvl < LOAD_LEVEL_NR; load_lvl++) {
>  		unsigned int reg, mask, val, offset = 0;
> @@ -142,6 +151,11 @@ static void __init armada37xx_cpufreq_dvfs_setup(struct regmap *base,
>  		mask = (ARMADA_37XX_NB_CLK_SEL_MASK
>  			<< ARMADA_37XX_NB_CLK_SEL_OFF);
>  
> +		/* Set TBG index, for all levels we use the same TBG */
> +		val = cpu_tbg_sel << ARMADA_37XX_NB_TBG_SEL_OFF;
> +		mask = (ARMADA_37XX_NB_TBG_SEL_MASK
> +			<< ARMADA_37XX_NB_TBG_SEL_OFF);
> +
>  		/*
>  		 * Set cpu divider based on the pre-computed array in
>  		 * order to have balanced step.
> @@ -160,14 +174,6 @@ static void __init armada37xx_cpufreq_dvfs_setup(struct regmap *base,
>  
>  		regmap_update_bits(base, reg, mask, val);
>  	}
> -
> -	/*
> -	 * Set cpu clock source, for all the level we keep the same
> -	 * clock source that the one already configured. For this one
> -	 * we need to use the clock framework
> -	 */
> -	parent = clk_get_parent(clk);
> -	clk_set_parent(clk, parent);
>  }
>  
>  /*
> @@ -358,11 +364,16 @@ static int __init armada37xx_cpufreq_driver_init(void)
>  	struct platform_device *pdev;
>  	unsigned long freq;
>  	unsigned int cur_frequency, base_frequency;
> -	struct regmap *nb_pm_base, *avs_base;
> +	struct regmap *nb_clk_base, *nb_pm_base, *avs_base;
>  	struct device *cpu_dev;
>  	int load_lvl, ret;
>  	struct clk *clk, *parent;
>  
> +	nb_clk_base =
> +		syscon_regmap_lookup_by_compatible("marvell,armada-3700-periph-clock-nb");
> +	if (IS_ERR(nb_clk_base))
> +		return -ENODEV;
> +
>  	nb_pm_base =
>  		syscon_regmap_lookup_by_compatible("marvell,armada-3700-nb-pm");
>  
> @@ -439,7 +450,7 @@ static int __init armada37xx_cpufreq_driver_init(void)
>  	armada37xx_cpufreq_avs_configure(avs_base, dvfs);
>  	armada37xx_cpufreq_avs_setup(avs_base, dvfs);
>  
> -	armada37xx_cpufreq_dvfs_setup(nb_pm_base, clk, dvfs->divider);
> +	armada37xx_cpufreq_dvfs_setup(nb_pm_base, nb_clk_base, dvfs->divider);
>  	clk_put(clk);
>  
>  	for (load_lvl = ARMADA_37XX_DVFS_LOAD_0; load_lvl < LOAD_LEVEL_NR;
> -- 
> 2.20.1
>

-- 
Gregory Clement, Bootlin
Embedded Linux and Kernel engineering
http://bootlin.com