linux-kernel - Re: [PATCH v2 2/3] clk: bcm2835: Support for clock parent selection

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Message-ID: <87egfn2m9y.fsf@eliezer.anholt.net>
Date:	Wed, 18 Nov 2015 10:30:17 -0800
From:	Eric Anholt <eric@...olt.net>
To:	Remi Pommarel <repk@...plefau.lt>,
	Stephen Warren <swarren@...dotorg.org>,
	Lee Jones <lee@...nel.org>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-rpi-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	Remi Pommarel <repk@...plefau.lt>
Subject: Re: [PATCH v2 2/3] clk: bcm2835: Support for clock parent selection

Remi Pommarel <repk@...plefau.lt> writes:

> Some bcm2835 clocks used by hardware (like "PWM" or "H264") can have multiple
> parent clocks. These clocks divide the rate of a parent which can be selected by
> setting the proper bits in the clock control register.
>
> Previously all these parents where handled by a mux clock. But a mux clock
> cannot be used because updating clock control register to select parent needs a
> password to be xor'd with the parent index.
>
> This patch get rid of mux clock and make these clocks handle their own parent,
> allowing them to select the one to use.
>
> Signed-off-by: Remi Pommarel <repk@...plefau.lt>
> ---
>  drivers/clk/bcm/clk-bcm2835.c | 122 ++++++++++++++++++++++++++----------------
>  1 file changed, 77 insertions(+), 45 deletions(-)
>
> diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
> index 1237716..2b01a53 100644
> --- a/drivers/clk/bcm/clk-bcm2835.c
> +++ b/drivers/clk/bcm/clk-bcm2835.c
> @@ -1198,16 +1198,6 @@ static long bcm2835_clock_rate_from_divisor(struct bcm2835_clock *clock,
>  	return temp;
>  }
>  
> -static long bcm2835_clock_round_rate(struct clk_hw *hw,
> -				     unsigned long rate,
> -				     unsigned long *parent_rate)
> -{
> -	struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw);
> -	u32 div = bcm2835_clock_choose_div(hw, rate, *parent_rate);
> -
> -	return bcm2835_clock_rate_from_divisor(clock, *parent_rate, div);
> -}
> -
>  static unsigned long bcm2835_clock_get_rate(struct clk_hw *hw,
>  					    unsigned long parent_rate)
>  {
> @@ -1279,13 +1269,75 @@ static int bcm2835_clock_set_rate(struct clk_hw *hw,
>  	return 0;
>  }
>  
> +static int bcm2835_clock_determine_rate(struct clk_hw *hw,
> +		struct clk_rate_request *req)
> +{
> +	struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw);
> +	struct clk_hw *parent, *best_parent = NULL;
> +	struct clk_rate_request parent_req;
> +	unsigned long rate, best_rate = 0;
> +	unsigned long prate, best_prate = 0;
> +	size_t i;
> +	u32 div;
> +
> +	/*
> +	 * Select parent clock that results in the closest but lower rate
> +	 */
> +	for (i = 0; i < clk_hw_get_num_parents(hw); ++i) {
> +		parent = clk_hw_get_parent_by_index(hw, i);
> +		if (!parent)
> +			continue;
> +		parent_req = *req;

parent_req appears dead, so it should be removed.

> +		prate = clk_hw_get_rate(parent);
> +		div = bcm2835_clock_choose_div(hw, req->rate, prate);
> +		rate = bcm2835_clock_rate_from_divisor(clock, prate, div);
> +		if (rate > best_rate && rate <= req->rate) {
> +			best_parent = parent;
> +			best_prate = prate;
> +			best_rate = rate;
> +		}
> +	}
> +
> +	if (!best_parent)
> +		return -EINVAL;
> +
> +	req->best_parent_hw = best_parent;
> +	req->best_parent_rate = best_prate;

I think you're supposed to req->rate = best_rate, here, too.  With these
two fixes,

Reviewed-by: Eric Anholt <eric@...olt.net>

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