linux-kernel - Re: [PATCH RFC v1 1/3] clk: divider: Add re-usable determine

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Date:   Tue, 18 May 2021 09:44:51 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        mturquette@...libre.com, sboyd@...nel.org, narmstrong@...libre.com,
        linux-clk@...r.kernel.org
Cc:     khilman@...libre.com, linux-kernel@...r.kernel.org,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RFC v1 1/3] clk: divider: Add re-usable determine_rate
 implementations


On Mon 17 May 2021 at 22:37, Martin Blumenstingl <martin.blumenstingl@...glemail.com> wrote:

> These are useful when running on 32-bit systems to increase the upper
> supported frequency limit. clk_ops.round_rate returns a signed long
> which limits the maximum rate on 32-bit systems to 2^31 (or approx.
> 2.14GHz). clk_ops.determine_rate internally uses an unsigned long so
> the maximum rate on 32-bit systems is 2^32 or approx. 4.29GHz.
>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
> ---
>  drivers/clk/clk-divider.c    | 39 +++++++++++++++++++++++++++++++++++-
>  include/linux/clk-provider.h |  6 ++++++
>  2 files changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> index 344997203f0e..24c94d2a3643 100644
> --- a/drivers/clk/clk-divider.c
> +++ b/drivers/clk/clk-divider.c
> @@ -377,7 +377,6 @@ long divider_ro_round_rate_parent(struct clk_hw *hw, struct clk_hw *parent,
>  }
>  EXPORT_SYMBOL_GPL(divider_ro_round_rate_parent);
>  
> -
>  static long clk_divider_round_rate(struct clk_hw *hw, unsigned long rate,
>  				unsigned long *prate)
>  {
> @@ -399,6 +398,44 @@ static long clk_divider_round_rate(struct clk_hw *hw, unsigned long rate,
>  				  divider->width, divider->flags);
>  }
>  
> +int divider_determine_rate(struct clk_hw *hw, struct clk_rate_request *req,
> +			   const struct clk_div_table *table, u8 width,
> +			   unsigned long flags)
> +{
> +	int div;
> +
> +	div = clk_divider_bestdiv(hw, req->best_parent_hw, req->rate,
> +				  &req->best_parent_rate, table, width, flags);
> +
> +	req->rate = DIV_ROUND_UP_ULL((u64)req->best_parent_rate, div);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(divider_determine_rate);
> +
> +int divider_ro_determine_rate(struct clk_hw *hw, struct clk_rate_request *req,
> +			      const struct clk_div_table *table, u8 width,
> +			      unsigned long flags, unsigned int val)
> +{
> +	int div;
> +
> +	div = _get_div(table, val, flags, width);
> +
> +	/* Even a read-only clock can propagate a rate change */
> +	if (clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT) {
> +		if (!req->best_parent_hw)
> +			return -EINVAL;
> +
> +		req->best_parent_rate = clk_hw_round_rate(req->best_parent_hw,
> +							  req->rate * div);
> +	}
> +
> +	req->rate = DIV_ROUND_UP_ULL((u64)req->best_parent_rate, div);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(divider_ro_determine_rate);

For a final version, could you factorize the code with the .round_rate()
variant ? It would remove a bit of duplication. 

Maybe determine_rate() can also replace round_rate() in the generic
divider ops ?

> +
>  int divider_get_val(unsigned long rate, unsigned long parent_rate,
>  		    const struct clk_div_table *table, u8 width,
>  		    unsigned long flags)
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index 162a2e5546a3..d83b829305c0 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -629,6 +629,12 @@ long divider_ro_round_rate_parent(struct clk_hw *hw, struct clk_hw *parent,
>  				  unsigned long rate, unsigned long *prate,
>  				  const struct clk_div_table *table, u8 width,
>  				  unsigned long flags, unsigned int val);
> +int divider_determine_rate(struct clk_hw *hw, struct clk_rate_request *req,
> +			   const struct clk_div_table *table, u8 width,
> +			   unsigned long flags);
> +int divider_ro_determine_rate(struct clk_hw *hw, struct clk_rate_request *req,
> +			      const struct clk_div_table *table, u8 width,
> +			      unsigned long flags, unsigned int val);
>  int divider_get_val(unsigned long rate, unsigned long parent_rate,
>  		const struct clk_div_table *table, u8 width,
>  		unsigned long flags);