Re: [PATCH mvebu v3 06/10] clk: mvebu: armada-37xx-periph: Fix workaround for switching from L1 to L0

Gregory CLEMENT
2021-03-29T14:49:52Z

Pali Rohár <pali@kernel.org> writes:

> When CPU frequency is at 250 MHz and set_rate() is called with 500 MHz (L1)
> quickly followed by a call with 1 GHz (L0), the CPU does not necessarily
> stay in L1 for at least 20ms as is required by Marvell errata.
>
> This situation happens frequently with the ondemand cpufreq governor and
> can be also reproduced with userspace governor. In most cases it causes CPU
> to crash.
>
> This change fixes the above issue and ensures that the CPU always stays in
> L1 for at least 20ms when switching from any state to L0.
>
> Signed-off-by: Marek Behún <kabel@kernel.org>
> Signed-off-by: Pali Rohár <pali@kernel.org>
> Acked-by: Stephen Boyd <sboyd@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: 61c40f35f5cd ("clk: mvebu: armada-37xx-periph: Fix switching CPU rate from 300Mhz to 1.2GHz")
> Cc: stable@vger.kernel.org

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

Thanks,

Gregory
> ---
> drivers/clk/mvebu/armada-37xx-periph.c | 45 ++++++++++++++++++++++----
> 1 file changed, 39 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/clk/mvebu/armada-37xx-periph.c b/drivers/clk/mvebu/armada-37xx-periph.c
> index b15e177bea7e..32ac6b6b7530 100644
> --- a/drivers/clk/mvebu/armada-37xx-periph.c
> +++ b/drivers/clk/mvebu/armada-37xx-periph.c
> @@ -84,6 +84,7 @@ struct clk_pm_cpu {
> void __iomem *reg_div;
> u8 shift_div;
> struct regmap *nb_pm_base;
> + unsigned long l1_expiration;
> };
>
> #define to_clk_double_div(_hw) container_of(_hw, struct clk_double_div, hw)
> @@ -504,22 +505,52 @@ static long clk_pm_cpu_round_rate(struct clk_hw *hw, unsigned long rate,
> * 2. Sleep 20ms for stabling VDD voltage
> * 3. Then switch from L1 (500/600 MHz) to L0 (1000/1200 MHz).
> */
> -static void clk_pm_cpu_set_rate_wa(unsigned long rate, struct regmap *base)
> +static void clk_pm_cpu_set_rate_wa(struct clk_pm_cpu *pm_cpu,
> + unsigned int new_level, unsigned long rate,
> + struct regmap *base)
> {
> unsigned int cur_level;
>
> - if (rate < 1000 * 1000 * 1000)
> - return;
> -
> regmap_read(base, ARMADA_37XX_NB_CPU_LOAD, &cur_level);
> cur_level &= ARMADA_37XX_NB_CPU_LOAD_MASK;
> - if (cur_level <= ARMADA_37XX_DVFS_LOAD_1)
> +
> + if (cur_level == new_level)
> + return;
> +
> + /*
> + * System wants to go to L1 on its own. If we are going from L2/L3,
> + * remember when 20ms will expire. If from L0, set the value so that
> + * next switch to L0 won't have to wait.
> + */
> + if (new_level == ARMADA_37XX_DVFS_LOAD_1) {
> + if (cur_level == ARMADA_37XX_DVFS_LOAD_0)
> + pm_cpu->l1_expiration = jiffies;
> + else
> + pm_cpu->l1_expiration = jiffies + msecs_to_jiffies(20);
> return;
> + }
> +
> + /*
> + * If we are setting to L2/L3, just invalidate L1 expiration time,
> + * sleeping is not needed.
> + */
> + if (rate < 1000*1000*1000)
> + goto invalidate_l1_exp;
> +
> + /*
> + * We are going to L0 with rate >= 1GHz. Check whether we have been at
> + * L1 for long enough time. If not, go to L1 for 20ms.
> + */
> + if (pm_cpu->l1_expiration && jiffies >= pm_cpu->l1_expiration)
> + goto invalidate_l1_exp;
>
> regmap_update_bits(base, ARMADA_37XX_NB_CPU_LOAD,
> ARMADA_37XX_NB_CPU_LOAD_MASK,
> ARMADA_37XX_DVFS_LOAD_1);
> msleep(20);
> +
> +invalidate_l1_exp:
> + pm_cpu->l1_expiration = 0;
> }
>
> static int clk_pm_cpu_set_rate(struct clk_hw *hw, unsigned long rate,
> @@ -553,7 +584,9 @@ static int clk_pm_cpu_set_rate(struct clk_hw *hw, unsigned long rate,
> reg = ARMADA_37XX_NB_CPU_LOAD;
> mask = ARMADA_37XX_NB_CPU_LOAD_MASK;
>
> - clk_pm_cpu_set_rate_wa(rate, base);
> + /* Apply workaround when base CPU frequency is 1000 or 1200 MHz */
> + if (parent_rate >= 1000*1000*1000)
> + clk_pm_cpu_set_rate_wa(pm_cpu, load_level, rate, base);
>
> regmap_update_bits(base, reg, mask, load_level);
>
> --
> 2.20.1
>

--
Gregory Clement, Bootlin
Embedded Linux and Kernel engineering