Re: [PATCH v2] clk: check the actual phase if get_phase is provided

Stephen Boyd
2016-02-25T23:15:01Z

On 02/18, Shawn Lin wrote:
> set_phase does sanity checking of degree and ask sub-driver
> to set the degree. If set_phase is limited to support the
> degree what the caller need, sub-driver may select a
> approximate value and return success state. In this case, it's
> inappropriate to assign the degree directly to clk->core->phase.
> We should ask sub-driver to decide the strategy. If sub-driver just
> want to support accurate degree, it can fail the set_phase. Otherwise,
> store the actual degree provided by sub-driver into clk->core->phase
> if get_phase is provided. Another improvemnt by this patch is that
> we can avoid to do unnecessary set_phase if the request defrees is
> already there.
>
> Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
>
> ---

Knee jerk reaction is why does the provider code set a phase that
isn't requested? Do we need some sort of clk_round_phase() API
that parallels clk_round_rate() so that drivers know what phase
they're going to get? Or do drivers not care what phase they get
when they call clk_set_phase()?

>
> Changes in v2:
> - remove actual_degree to simplify the changes
> - bail early if nothing to to
>
> drivers/clk/clk.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index b4db67a..275e70f 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1902,6 +1902,10 @@ int clk_set_phase(struct clk *clk, int degrees)
>
> clk_prepare_lock();
>
> + /* bail early if nothing to do */
> + if (degrees == clk->core->phase)
> + goto out;
> +

This could be split out into a different "optimization" patch and
applied today.

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