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

[Sascha Hauer <s.hauer@pengutronix.de>]

On Sat, Aug 11, 2018 at 12:35:39PM -0700, Andrey Smirnov wrote:
> 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.

Applied now, thanks

Sascha


-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

_______________________________________________
barebox mailing list
barebox@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/barebox