[03/13] clk: implement clk_hw_set_rate()

Commit Message

Benjamin Bara Sept. 17, 2023, 10:39 p.m. UTC

From: Benjamin Bara <[e-mail]>

This function can be used to set the rate of a clock hardware from a
driver, e.g. to adapt the rate to a clock change coming from the parent.

Signed-off-by: Benjamin Bara <[e-mail]>
---
 drivers/clk/clk.c            | 15 +++++++++++++++
 include/linux/clk-provider.h |  1 +
 2 files changed, 16 insertions(+)

Comments

Maxime Ripard Sept. 19, 2023, 6:50 a.m. UTC | #1

Hi,

On Mon, Sep 18, 2023 at 12:39:59AM +0200, Benjamin Bara wrote:
> From: Benjamin Bara <[e-mail]>
> 
> This function can be used to set the rate of a clock hardware from a
> driver, e.g. to adapt the rate to a clock change coming from the parent.
> 
> Signed-off-by: Benjamin Bara <[e-mail]>
> ---
>  drivers/clk/clk.c            | 15 +++++++++++++++
>  include/linux/clk-provider.h |  1 +
>  2 files changed, 16 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index c249f9791ae8..3e222802b712 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -2462,6 +2462,21 @@ static int clk_core_set_rate_nolock(struct clk_core *core,
>  	return ret;
>  }
>  
> +int clk_hw_set_rate(struct clk_hw *hw, unsigned long req_rate)
> +{
> +	/* A rate change is ongoing, so just target the required rate.
> +	 * Note: this does not work if one clock along the line has
> +	 * CLK_RECALC_NEW_RATES active, as this overwrites the new_rate again.
> +	 */
> +	if (hw->core->new_rate != hw->core->rate) {
> +		hw->core->new_rate = req_rate;
> +		return 0;
> +	}
> +
> +	return clk_core_set_rate_nolock(hw->core, req_rate);
> +}
> +EXPORT_SYMBOL_GPL(clk_hw_set_rate);

So, we discussed it recently, and it's non-obvious to see how it would
work if you're in a set_rate change that modifies the tree and the new
call to clk_hw_set_rate modifies the tree too. Some explanation on how
it's handled, and some unit tests are required here imo.

Maxime

Patch

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index c249f9791ae8..3e222802b712 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -2462,6 +2462,21 @@  static int clk_core_set_rate_nolock(struct clk_core *core,
 	return ret;
 }
 
+int clk_hw_set_rate(struct clk_hw *hw, unsigned long req_rate)
+{
+	/* A rate change is ongoing, so just target the required rate.
+	 * Note: this does not work if one clock along the line has
+	 * CLK_RECALC_NEW_RATES active, as this overwrites the new_rate again.
+	 */
+	if (hw->core->new_rate != hw->core->rate) {
+		hw->core->new_rate = req_rate;
+		return 0;
+	}
+
+	return clk_core_set_rate_nolock(hw->core, req_rate);
+}
+EXPORT_SYMBOL_GPL(clk_hw_set_rate);
+
 /**
  * clk_set_rate - specify a new rate for clk
  * @clk: the clk whose rate is being changed
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index ec32ec58c59f..3fb99ed5e8d9 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -1316,6 +1316,7 @@  int clk_hw_get_parent_index(struct clk_hw *hw);
 int clk_hw_set_parent(struct clk_hw *hw, struct clk_hw *new_parent);
 unsigned int __clk_get_enable_count(struct clk *clk);
 unsigned long clk_hw_get_rate(const struct clk_hw *hw);
+int clk_hw_set_rate(struct clk_hw *hw, unsigned long req_rate);
 unsigned long clk_hw_get_flags(const struct clk_hw *hw);
 #define clk_hw_can_set_rate_parent(hw) \
 	(clk_hw_get_flags((hw)) & CLK_SET_RATE_PARENT)