linux-kernel - Re: [PATCH] clk: Ensure correct consumer's rate boundaries

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Message-ID: <aWpq4E4_zTIO8Phr@redhat.com>
Date: Fri, 16 Jan 2026 11:44:16 -0500
From: Brian Masney <bmasney@...hat.com>
To: Chuan Liu <chuan.liu@...ogic.com>
Cc: Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, linux-clk@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: Ensure correct consumer's rate boundaries

Hi Chuan,
i
On Fri, Jan 16, 2026 at 05:32:39PM +0800, Chuan Liu wrote:
> On 1/15/2026 9:01 PM, Brian Masney wrote:
> > On Thu, Jan 15, 2026 at 10:37:55AM +0800, Chuan Liu wrote:
> > > On 1/15/2026 9:30 AM, Brian Masney wrote:
> > > > On Fri, Jan 09, 2026 at 11:24:22AM +0800, Chuan Liu via B4 Relay wrote:
> > > > > From: Chuan Liu <chuan.liu@...ogic.com>
> > > > > 
> > > > > If we were to have two users of the same clock, doing something like:
> > > > > 
> > > > > clk_set_rate_range(user1, 1000, 2000);
> > > > > clk_set_rate_range(user2, 3000, 4000);
> > > > > 
> > > > > Even when user2's call returns -EINVAL, the min_rate and max_rate of
> > > > > user2 are still incorrectly updated. This causes subsequent calls by
> > > > > user1 to fail when setting the clock rate, as clk_core_get_boundaries()
> > > > > returns corrupted boundaries (min_rate = 3000, max_rate = 2000).
> > > > > 
> > > > > To prevent this, clk_core_check_boundaries() now rollback to the old
> > > > > boundaries when the check fails.
> > > > > 
> > > > > Signed-off-by: Chuan Liu <chuan.liu@...ogic.com>
> > > > > ---
> > > > >    drivers/clk/clk.c | 8 ++++++--
> > > > >    1 file changed, 6 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > > > > index 85d2f2481acf..0dfb16bf3f31 100644
> > > > > --- a/drivers/clk/clk.c
> > > > > +++ b/drivers/clk/clk.c
> > > > > @@ -2710,13 +2710,17 @@ static int clk_set_rate_range_nolock(struct clk *clk,
> > > > >          */
> > > > >         rate = clamp(rate, min, max);
> > > > >         ret = clk_core_set_rate_nolock(clk->core, rate);
> > > > > +
> > > > > +out:
> > > > >         if (ret) {
> > > > > -             /* rollback the changes */
> > > > > +             /*
> > > > > +              * Rollback the consumer’s old boundaries if check_boundaries or
> > > > > +              * set_rate fails.
> > > > > +              */
> > > > >                 clk->min_rate = old_min;
> > > > >                 clk->max_rate = old_max;
> > > > >         }
> > > > > 
> > > > > -out:
> > > > >         if (clk->exclusive_count)
> > > > >                 clk_core_rate_protect(clk->core);
> > > > 
> > > > This looks correct to me. Just a quick question though to possibly
> > > > simplify this further. Currently clk_set_rate_range_nolock() has the
> > > > following code:
> > > > 
> > > >           /* Save the current values in case we need to rollback the change */
> > > >           old_min = clk->min_rate;
> > > >           old_max = clk->max_rate;
> > > >           clk->min_rate = min;
> > > >           clk->max_rate = max;
> > > > 
> > > >           if (!clk_core_check_boundaries(clk->core, min, max)) {
> > > >                   ret = -EINVAL;
> > > >                   goto out;
> > > >           }
> > > > 
> > > > Since clk_core_check_boundaries() is a readonly operation, what do you
> > > > think about moving clk_core_check_boundaries above the code that saves the
> > > > previous values? That way we only need to rollback in the case where
> > > > set_rate() fails.
> > > > 
> > > 
> > > Perhaps it would be more appropriate to move the clk_core_check_boundaries()
> > > check before saving the previous values, like this:
> > > 
> > >        if (!clk_core_check_boundaries(clk->core, min, max)) {
> > >                ret = -EINVAL;
> > >                goto out;
> > >        }
> > > 
> > >        /* Save the current values in case we need to rollback the change */
> > >        old_min = clk->min_rate;
> > >        old_max = clk->max_rate;
> > >        clk->min_rate = min;
> > >        clk->max_rate = max;
> > 
> > Yes, that's what I had in mind.
> > 
> > > The changes in this patch are intended to avoid altering the original driver
> > > execution flow, while making the minimal modification to fix the issue where
> > > the range is incorrectly assigned.
> > 
> > It's ultimately up to Stephen what he wants to take. I personally have a
> > slight preference to the approach above, however I don't have a strong
> > opinion about it. I'm just calling this out to help with reviews.
> > 
> > The one thing that Stephen will want though is kunit tests for this
> > since it changes the clk core. There's already a bunch of kunit tests in
> > drivers/clk/clk_test.c. Feel free to reach out to me if you need help
> > writing a new test.
> > 
> 
> Thank you for the reminder. Stephen previously pointed out the need to
> improve the kunit tests, and I will take this into account in future
> submissions.
> 
> I would greatly appreciate it if you could help enhance the kunit tests for
> this particular test case.:)

I attached a patch that adds a kunit test that you can apply with 'git
am'. Try it with, and without your patch to see how it operates with
and without your fix. If you like it, then feel free to include it in
the next version of this patch series.

Brian

View attachment "0001-clk-test-introduce-test-to-test-the-rollback-of-cons.patch" of type "text/plain" (3007 bytes)