Re: [PATCH v4 03/10] clk: Use clamp instead of open-coding our own

From: Maxime Ripard <maxime@cerno.tech>
To: Stephen Boyd <sboyd@kernel.org>
Cc: Mike Turquette <mturquette@baylibre.com>,
	linux-clk@vger.kernel.org, dri-devel@lists.freedesktop.org,
	Dave Stevenson <dave.stevenson@raspberrypi.com>,
	Phil Elwell <phil@raspberrypi.com>,
	Tim Gover <tim.gover@raspberrypi.com>,
	Dom Cobley <dom@raspberrypi.com>
Subject: Re: [PATCH v4 03/10] clk: Use clamp instead of open-coding our own
Date: Mon, 21 Feb 2022 17:30:01 +0100	[thread overview]
Message-ID: <20220221163001.k4nstaxtbmlxgz3j@houat> (raw)
In-Reply-To: <20220218223422.4FA9DC340E9@smtp.kernel.org>

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On Fri, Feb 18, 2022 at 02:34:20PM -0800, Stephen Boyd wrote:
> Quoting Maxime Ripard (2022-01-25 06:15:42)
> > The code in clk_set_rate_range() will, if the current rate is outside of
> > the new range, will force it to the minimum or maximum. This is
> > equivalent to using clamp, while being less readable. Let's switch to
> > using clamp instead.
> > 
> > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> > ---
> >  drivers/clk/clk.c | 6 +-----
> >  1 file changed, 1 insertion(+), 5 deletions(-)
> > 
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > index 7bb5ae0fb688..150d1bc0985b 100644
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -2365,11 +2365,7 @@ int clk_set_rate_range(struct clk *clk, unsigned long min, unsigned long max)
> >                  *   this corner case when determining the rate
> >                  */
> >  
> > -               if (rate < min)
> > -                       rate = min;
> > -               else
> > -                       rate = max;
> > -
> > +               rate = clamp(clk->core->req_rate, min, max);
> 
> This isn't equivalent. The else arm is taken if rate >= min and rate is
> set to max, whereas clamp() will leave the rate unchanged if rate >= min
> && rate < max.

This can't happen, since we're in an if block that is (rate < min ||
rate > max), so at this point if rate is not less than min, it is
greater than rate. Thus, it's equivalent to clamp.

Still, the commit message could be better, I'll rephrase it.

Maxime

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