Re: [PATCH] serial: lpuart: Avoid division by zero when requested baudrate is

[Andrey Smirnov <andrew.smirnov@gmail.com>]

On Mon, May 14, 2018 at 11:07 PM Sascha Hauer <s.hauer@pengutronix.de> wrote:
>
> On Mon, May 14, 2018 at 05:20:56PM -0700, Andrey Smirnov wrote:
> > On Mon, May 14, 2018 at 12:14 AM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> > > On Tue, May 08, 2018 at 02:15:02PM -0700, Andrey Smirnov wrote:
> > >> With serdev device support added there's now a corner case where:
> > >>
> > >>  1. There is a DT node for a serdev device on one of the UARTs
> > >>  2. There is no driver that binds against serdev device's compatibility
> > >>     string
> > >>
> > >> with 1 and 2 being true it is possible to end up in a situation where
> > >> a particualr UART has not been initalized to any baudrate when
> > >> clock_notifier_call_chain() gets called. This effectively translates
> > >> to
> > >>
> > >>       set_baudrate(uart, 0);
> > >>
> > >> which for LPUART driver result in a division by zero.
> > >
> > > This probably leads to a division by zero for most drivers since
> > > dividing by the baudrate is a common pattern. Wouldn't it be better to
> > > catch this is console_set_baudrate()?
> > >
> >
> > It would, but none of the drivers that register a callback with
> > clock_register_client() (serial_imx.c, serial_auart.c, stm-serial.c,
> > serial_lpuart.c and serial_cadence.c) use console_set_badrate() and
> > instead call ->setbrg() directly. Probably because
> > console_set_baudrate() also handles interactive baudrate switch for
> > f_active console devices. Serial_imx.c doesn't preform any division,
> > so it is safe and I can go through the rest of them to add appropriate
> > checks? Another option is probably to try to come up with common
> > clock_register_client() infrastructure(since all of the handlers are
> > the same) and keep that check there.
> >
> > Let me know if you want me to do either.
>
> I see. For the sake of simplicity I think we can go with your original
> patch. In the auart and cadence driver the clock notify stuff is unused,
> only copy paste leftover from copying the i.MX driver. That leaves the
> lpuart driver which really has this problem.
>

Sascha, I don't think this patch ever made it into master. I am
assuming it just slipped through the cracks. Let me know if anything
needs changing for it to be applied.

Thanks,
Andrey Smirnov

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