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

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Date:   Mon, 29 Mar 2021 16:49:08 +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 06/10] clk: mvebu: armada-37xx-periph: Fix
 workaround for switching from L1 to L0

Pali Rohár <pali@...nel.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@...nel.org>
> Signed-off-by: Pali Rohár <pali@...nel.org>
> Acked-by: Stephen Boyd <sboyd@...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: 61c40f35f5cd ("clk: mvebu: armada-37xx-periph: Fix switching CPU rate from 300Mhz to 1.2GHz")
> Cc: stable@...r.kernel.org

Acked-by: Gregory CLEMENT <gregory.clement@...tlin.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
http://bootlin.com