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Date: Mon, 29 Mar 2021 16:45:53 +0200
From: Gregory CLEMENT <gregory.clement@...tlin.com>
To: Pali Rohár <pali@...nel.org>,
Andrew Lunn <andrew@...n.ch>,
Michael Turquette <mturquette@...libre.com>,
Stephen Boyd <sboyd@...nel.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-clk@...r.kernel.org
Cc: Marek Behún <kabel@...nel.org>,
Miquel Raynal <miquel.raynal@...tlin.com>,
Tomasz Maciej Nowak <tmn505@...il.com>,
Luka Perkov <luka.perkov@...tura.hr>,
Andre Heider <a.heider@...il.com>,
Vladimir Vid <vladimir.vid@...tura.hr>,
Russell King <rmk+kernel@...linux.org.uk>,
Gérald Kerma <gerald@....net>,
Konstantin Porotchkin <kostap@...vell.com>
Subject: Re: [PATCH mvebu v3 02/10] cpufreq: armada-37xx: Fix setting TBG
parent for load levels
Pali Rohár <pali@...nel.org> writes:
> From: Marek Behún <kabel@...nel.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@...nel.org>
> Tested-by: Pali Rohár <pali@...nel.org>
> Tested-by: Tomasz Maciej Nowak <tmn505@...il.com>
> Tested-by: Anders Trier Olesen <anders.trier.olesen@...il.com>
> Tested-by: Philip Soares <philips@...isense.com>
> Fixes: 92ce45fb875d ("cpufreq: Add DVFS support for Armada 37xx")
> Cc: stable@...r.kernel.org
Acked-by: Gregory CLEMENT <gregory.clement@...tlin.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
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