linux-kernel - Re: [PATCH v2] clk: check the actual phase if get

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Date:	Thu, 25 Feb 2016 15:14:58 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Shawn Lin <shawn.lin@...k-chips.com>
Cc:	Michael Turquette <mturquette@...libre.com>,
	linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] clk: check the actual phase if get_phase is provided

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@...k-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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