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

Eric Anholt
2015-11-18T18:30:22Z

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Remi Pommarel <repk@triplefau.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@triplefau.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@anholt.net>

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