[PATCH 1/4] nvmem: rockchip-otp: Serialize reads

[Alexey Charkov]

On Wed, Sep 2, 2026 at 2:17 PM Miquel Raynal <miquel.raynal at bootlin.com> wrote:
>
> On 02/09/2026 at 13:24:00 +04, Alexey Charkov <alchark at flipper.net> wrote:
>
> > On Wed, Sep 2, 2026 at 1:10 PM Miquel Raynal <miquel.raynal at bootlin.com> wrote:
> >>
> >> On 01/09/2026 at 19:33:11 +04, Alexey Charkov <alchark at flipper.net> wrote:
> >>
> >> > The OTP controller is driven through a single set of registers holding a
> >> > state machine which has to be stepped through for every word read, yet
> >> > nothing keeps two readers out of each other's way. Concurrent reads
> >> > interleave, and the outcome is either a reader bailing out:
> >> >
> >> >   rockchip-otp 2a580000.otp: timeout during read setup
> >> >
> >> > or, worse, one of them silently taking delivery of the other's data.
> >> >
> >> > Reading two cells in parallel from userspace on RK3576 reproduces both
> >> > within 150 iterations - 53 read errors and 9 corrupted results, the latter
> >> > either losing their first word or, in one case, ending in the two bytes
> >> > which belong to the other reader's cell - whereas the same reads issued
> >> > sequentially never fail. Concurrency is not hypothetical here, as six
> >> > thermal sensors source their trim values from the OTP and reach the driver
> >> > straight from asynchronous driver probing.
> >> >
> >> > Guard the read path with a mutex. Reads are the only way into the hardware,
> >> > as the driver registers no write callback, and they always run in process
> >> > context, so a plain mutex spanning the whole clock-enable, read,
> >> > clock-disable sequence is enough.
> >> >
> >> > Fixes: 755864feb729 ("nvmem: add Rockchip OTP driver")
> >> > Cc: stable at vger.kernel.org
> >> > Signed-off-by: Alexey Charkov <alchark at flipper.net>
> >>
> >> Reviewed-by: Miquel Raynal <miquel.raynal at bootlin.com>
> >
> > Thanks for your review Miquel!
> >
> > Sashiko complained about mixing a scope-based guard into a function
> > with goto-based error handling, so I am replacing the guard(mutex)
> > with explicit lock and unlock calls for v2. There won't be any
> > semantic change though, so if you don't mind I'd like to carry your
> > tag into the v2 version.
>
> Of course.

Thank you!

> I haven't seen Sashiko's answer but isn't the goal of guards to just be
> released whatever the actual return path?

I believe it's based on the guidance in [1]. In this particular case,
gotos don't jump outside the scope where I put the guard, so the
scope-based guard is still correct. However, stylistically, it is
indeed uncommon to see scope-based guards in functions using gotos.
Explicit lock/unlock is easy in this case, anyway.

[1] https://elixir.bootlin.com/linux/v7.2.2/source/include/linux/cleanup.h#L148-L153

Best regards,
Alexey