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Date:   Fri, 15 Oct 2021 10:01:38 +0200
From:   Nicolas Ferre <nicolas.ferre@...rochip.com>
To:     Claudiu Beznea <claudiu.beznea@...rochip.com>,
        <mturquette@...libre.com>, <sboyd@...nel.org>,
        <alexandre.belloni@...tlin.com>, <ludovic.desroches@...rochip.com>
CC:     <linux-clk@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 11/15] clk: at91: clk-sam9x60-pll: add notifier for div
 part of PLL

On 11/10/2021 at 13:27, Claudiu Beznea wrote:
> SAM9X60's PLL which is also part of SAMA7G5 is composed of 2 parts:
> one fractional part and one divider. On SAMA7G5 the CPU PLL could be
> changed at run-time to implement DVFS. The hardware clock tree on
> SAMA7G5 for CPU PLL is as follows:
> 
>                         +---- div1 ----------------> cpuck
>                         |
> FRAC PLL ---> DIV PLL -+-> prescaler ---> div0 ---> mck0
> 
> The div1 block is not implemented in Linux; on prescaler block it has
> been discovered a bug on some scenarios and will be removed from Linux
> in next commits. Thus, the final clock tree that will be used in Linux
> will be as follows:
> 
>                         +-----------> cpuck
>                         |
> FRAC PLL ---> DIV PLL -+-> div0 ---> mck0
> 
> It has been proposed in [1] to not introduce a new CPUFreq driver but
> to overload the proper clock drivers with proper operation such that
> cpufreq-dt to be used. To accomplish this DIV PLL and div0 implement
> clock notifiers which applies safe dividers before FRAC PLL is changed.
> The current commit treats only the DIV PLL by adding a notifier that
> sets a safe divider on PRE_RATE_CHANGE events. The safe divider is
> provided by initialization clock code (sama7g5.c). The div0 is treated
> in next commits (to keep the changes as clean as possible).
> 
> [1] https://lore.kernel.org/lkml/20210105104426.4tmgc2l3vyicwedd@vireshk-i7/
> 
> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>

Yes, it's needed:
Acked-by: Nicolas Ferre <nicolas.ferre@...rochip.com>

> ---
>   drivers/clk/at91/clk-sam9x60-pll.c | 102 ++++++++++++++++++++++-------
>   drivers/clk/at91/pmc.h             |   3 +-
>   drivers/clk/at91/sam9x60.c         |   6 +-
>   drivers/clk/at91/sama7g5.c         |  13 +++-
>   4 files changed, 95 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/clk/at91/clk-sam9x60-pll.c b/drivers/clk/at91/clk-sam9x60-pll.c
> index a73d7c96ce1d..d757003004cb 100644
> --- a/drivers/clk/at91/clk-sam9x60-pll.c
> +++ b/drivers/clk/at91/clk-sam9x60-pll.c
> @@ -5,6 +5,7 @@
>    */
>   
>   #include <linux/bitfield.h>
> +#include <linux/clk.h>
>   #include <linux/clk-provider.h>
>   #include <linux/clkdev.h>
>   #include <linux/clk/at91_pmc.h>
> @@ -47,12 +48,15 @@ struct sam9x60_div {
>   	struct sam9x60_pll_core core;
>   	struct at91_clk_pms pms;
>   	u8 div;
> +	u8 safe_div;
>   };
>   
>   #define to_sam9x60_pll_core(hw)	container_of(hw, struct sam9x60_pll_core, hw)
>   #define to_sam9x60_frac(core)	container_of(core, struct sam9x60_frac, core)
>   #define to_sam9x60_div(core)	container_of(core, struct sam9x60_div, core)
>   
> +static struct sam9x60_div *notifier_div;
> +
>   static inline bool sam9x60_pll_ready(struct regmap *regmap, int id)
>   {
>   	unsigned int status;
> @@ -329,6 +333,26 @@ static const struct clk_ops sam9x60_frac_pll_ops_chg = {
>   	.restore_context = sam9x60_frac_pll_restore_context,
>   };
>   
> +/* This function should be called with spinlock acquired. */
> +static void sam9x60_div_pll_set_div(struct sam9x60_pll_core *core, u32 div,
> +				    bool enable)
> +{
> +	struct regmap *regmap = core->regmap;
> +	u32 ena_msk = enable ? core->layout->endiv_mask : 0;
> +	u32 ena_val = enable ? (1 << core->layout->endiv_shift) : 0;
> +
> +	regmap_update_bits(regmap, AT91_PMC_PLL_CTRL0,
> +			   core->layout->div_mask | ena_msk,
> +			   (div << core->layout->div_shift) | ena_val);
> +
> +	regmap_update_bits(regmap, AT91_PMC_PLL_UPDT,
> +			   AT91_PMC_PLL_UPDT_UPDATE | AT91_PMC_PLL_UPDT_ID_MSK,
> +			   AT91_PMC_PLL_UPDT_UPDATE | core->id);
> +
> +	while (!sam9x60_pll_ready(regmap, core->id))
> +		cpu_relax();
> +}
> +
>   static int sam9x60_div_pll_set(struct sam9x60_pll_core *core)
>   {
>   	struct sam9x60_div *div = to_sam9x60_div(core);
> @@ -346,17 +370,7 @@ static int sam9x60_div_pll_set(struct sam9x60_pll_core *core)
>   	if (!!(val & core->layout->endiv_mask) && cdiv == div->div)
>   		goto unlock;
>   
> -	regmap_update_bits(regmap, AT91_PMC_PLL_CTRL0,
> -			   core->layout->div_mask | core->layout->endiv_mask,
> -			   (div->div << core->layout->div_shift) |
> -			   (1 << core->layout->endiv_shift));
> -
> -	regmap_update_bits(regmap, AT91_PMC_PLL_UPDT,
> -			   AT91_PMC_PLL_UPDT_UPDATE | AT91_PMC_PLL_UPDT_ID_MSK,
> -			   AT91_PMC_PLL_UPDT_UPDATE | core->id);
> -
> -	while (!sam9x60_pll_ready(regmap, core->id))
> -		cpu_relax();
> +	sam9x60_div_pll_set_div(core, div->div, 1);
>   
>   unlock:
>   	spin_unlock_irqrestore(core->lock, flags);
> @@ -502,16 +516,7 @@ static int sam9x60_div_pll_set_rate_chg(struct clk_hw *hw, unsigned long rate,
>   	if (cdiv == div->div)
>   		goto unlock;
>   
> -	regmap_update_bits(regmap, AT91_PMC_PLL_CTRL0,
> -			   core->layout->div_mask,
> -			   (div->div << core->layout->div_shift));
> -
> -	regmap_update_bits(regmap, AT91_PMC_PLL_UPDT,
> -			   AT91_PMC_PLL_UPDT_UPDATE | AT91_PMC_PLL_UPDT_ID_MSK,
> -			   AT91_PMC_PLL_UPDT_UPDATE | core->id);
> -
> -	while (!sam9x60_pll_ready(regmap, core->id))
> -		cpu_relax();
> +	sam9x60_div_pll_set_div(core, div->div, 0);
>   
>   unlock:
>   	spin_unlock_irqrestore(core->lock, irqflags);
> @@ -538,6 +543,48 @@ static void sam9x60_div_pll_restore_context(struct clk_hw *hw)
>   		sam9x60_div_pll_set(core);
>   }
>   
> +static int sam9x60_div_pll_notifier_fn(struct notifier_block *notifier,
> +				       unsigned long code, void *data)
> +{
> +	struct sam9x60_div *div = notifier_div;
> +	struct sam9x60_pll_core core = div->core;
> +	struct regmap *regmap = core.regmap;
> +	unsigned long irqflags;
> +	u32 val, cdiv;
> +	int ret = NOTIFY_DONE;
> +
> +	if (code != PRE_RATE_CHANGE)
> +		return ret;
> +
> +	/*
> +	 * We switch to safe divider to avoid overclocking of other domains
> +	 * feed by us while the frac PLL (our parent) is changed.
> +	 */
> +	div->div = div->safe_div;
> +
> +	spin_lock_irqsave(core.lock, irqflags);
> +	regmap_update_bits(regmap, AT91_PMC_PLL_UPDT, AT91_PMC_PLL_UPDT_ID_MSK,
> +			   core.id);
> +	regmap_read(regmap, AT91_PMC_PLL_CTRL0, &val);
> +	cdiv = (val & core.layout->div_mask) >> core.layout->div_shift;
> +
> +	/* Stop if nothing changed. */
> +	if (cdiv == div->safe_div)
> +		goto unlock;
> +
> +	sam9x60_div_pll_set_div(&core, div->div, 0);
> +	ret = NOTIFY_OK;
> +
> +unlock:
> +	spin_unlock_irqrestore(core.lock, irqflags);
> +
> +	return ret;
> +}
> +
> +static struct notifier_block sam9x60_div_pll_notifier = {
> +	.notifier_call = sam9x60_div_pll_notifier_fn,
> +};
> +
>   static const struct clk_ops sam9x60_div_pll_ops = {
>   	.prepare = sam9x60_div_pll_prepare,
>   	.unprepare = sam9x60_div_pll_unprepare,
> @@ -647,7 +694,8 @@ struct clk_hw * __init
>   sam9x60_clk_register_div_pll(struct regmap *regmap, spinlock_t *lock,
>   			     const char *name, const char *parent_name, u8 id,
>   			     const struct clk_pll_characteristics *characteristics,
> -			     const struct clk_pll_layout *layout, u32 flags)
> +			     const struct clk_pll_layout *layout, u32 flags,
> +			     u32 safe_div)
>   {
>   	struct sam9x60_div *div;
>   	struct clk_hw *hw;
> @@ -656,9 +704,13 @@ sam9x60_clk_register_div_pll(struct regmap *regmap, spinlock_t *lock,
>   	unsigned int val;
>   	int ret;
>   
> -	if (id > PLL_MAX_ID || !lock)
> +	/* We only support one changeable PLL. */
> +	if (id > PLL_MAX_ID || !lock || (safe_div && notifier_div))
>   		return ERR_PTR(-EINVAL);
>   
> +	if (safe_div >= PLL_DIV_MAX)
> +		safe_div = PLL_DIV_MAX - 1;
> +
>   	div = kzalloc(sizeof(*div), GFP_KERNEL);
>   	if (!div)
>   		return ERR_PTR(-ENOMEM);
> @@ -678,6 +730,7 @@ sam9x60_clk_register_div_pll(struct regmap *regmap, spinlock_t *lock,
>   	div->core.layout = layout;
>   	div->core.regmap = regmap;
>   	div->core.lock = lock;
> +	div->safe_div = safe_div;
>   
>   	spin_lock_irqsave(div->core.lock, irqflags);
>   
> @@ -693,6 +746,9 @@ sam9x60_clk_register_div_pll(struct regmap *regmap, spinlock_t *lock,
>   	if (ret) {
>   		kfree(div);
>   		hw = ERR_PTR(ret);
> +	} else if (div->safe_div) {
> +		notifier_div = div;
> +		clk_notifier_register(hw->clk, &sam9x60_div_pll_notifier);
>   	}
>   
>   	return hw;
> diff --git a/drivers/clk/at91/pmc.h b/drivers/clk/at91/pmc.h
> index 45df094498ce..207ecccef29f 100644
> --- a/drivers/clk/at91/pmc.h
> +++ b/drivers/clk/at91/pmc.h
> @@ -214,7 +214,8 @@ struct clk_hw * __init
>   sam9x60_clk_register_div_pll(struct regmap *regmap, spinlock_t *lock,
>   			     const char *name, const char *parent_name, u8 id,
>   			     const struct clk_pll_characteristics *characteristics,
> -			     const struct clk_pll_layout *layout, u32 flags);
> +			     const struct clk_pll_layout *layout, u32 flags,
> +			     u32 safe_div);
>   
>   struct clk_hw * __init
>   sam9x60_clk_register_frac_pll(struct regmap *regmap, spinlock_t *lock,
> diff --git a/drivers/clk/at91/sam9x60.c b/drivers/clk/at91/sam9x60.c
> index 5f6fa89571b7..5c264185f261 100644
> --- a/drivers/clk/at91/sam9x60.c
> +++ b/drivers/clk/at91/sam9x60.c
> @@ -242,7 +242,7 @@ static void __init sam9x60_pmc_setup(struct device_node *np)
>   					    * This feeds CPU. It should not
>   					    * be disabled.
>   					    */
> -					  CLK_IS_CRITICAL | CLK_SET_RATE_GATE);
> +					  CLK_IS_CRITICAL | CLK_SET_RATE_GATE, 0);
>   	if (IS_ERR(hw))
>   		goto err_free;
>   
> @@ -260,7 +260,7 @@ static void __init sam9x60_pmc_setup(struct device_node *np)
>   					  &pll_div_layout,
>   					  CLK_SET_RATE_GATE |
>   					  CLK_SET_PARENT_GATE |
> -					  CLK_SET_RATE_PARENT);
> +					  CLK_SET_RATE_PARENT, 0);
>   	if (IS_ERR(hw))
>   		goto err_free;
>   
> @@ -279,7 +279,7 @@ static void __init sam9x60_pmc_setup(struct device_node *np)
>   	hw = at91_clk_register_master_div(regmap, "masterck_div",
>   					  "masterck_pres", &sam9x60_master_layout,
>   					  &mck_characteristics, &mck_lock,
> -					  CLK_SET_RATE_GATE);
> +					  CLK_SET_RATE_GATE, 0);
>   	if (IS_ERR(hw))
>   		goto err_free;
>   
> diff --git a/drivers/clk/at91/sama7g5.c b/drivers/clk/at91/sama7g5.c
> index 970135e19a75..ae52c10af040 100644
> --- a/drivers/clk/at91/sama7g5.c
> +++ b/drivers/clk/at91/sama7g5.c
> @@ -127,6 +127,8 @@ static const struct clk_pll_characteristics pll_characteristics = {
>    * @t:		clock type
>    * @f:		clock flags
>    * @eid:	export index in sama7g5->chws[] array
> + * @safe_div:	intermediate divider need to be set on PRE_RATE_CHANGE
> + *		notification
>    */
>   static const struct {
>   	const char *n;
> @@ -136,6 +138,7 @@ static const struct {
>   	unsigned long f;
>   	u8 t;
>   	u8 eid;
> +	u8 safe_div;
>   } sama7g5_plls[][PLL_ID_MAX] = {
>   	[PLL_ID_CPU] = {
>   		{ .n = "cpupll_fracck",
> @@ -156,7 +159,12 @@ static const struct {
>   		  .t = PLL_TYPE_DIV,
>   		   /* This feeds CPU. It should not be disabled. */
>   		  .f = CLK_IS_CRITICAL | CLK_SET_RATE_PARENT,
> -		  .eid = PMC_CPUPLL, },
> +		  .eid = PMC_CPUPLL,
> +		  /*
> +		   * Safe div=15 should be safe even for switching b/w 1GHz and
> +		   * 90MHz (frac pll might go up to 1.2GHz).
> +		   */
> +		  .safe_div = 15, },
>   	},
>   
>   	[PLL_ID_SYS] = {
> @@ -967,7 +975,8 @@ static void __init sama7g5_pmc_setup(struct device_node *np)
>   					sama7g5_plls[i][j].p, i,
>   					sama7g5_plls[i][j].c,
>   					sama7g5_plls[i][j].l,
> -					sama7g5_plls[i][j].f);
> +					sama7g5_plls[i][j].f,
> +					sama7g5_plls[i][j].safe_div);
>   				break;
>   
>   			default:
> 


-- 
Nicolas Ferre

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