RE: [PATCH v2 1/2] serial: sh-sci: Avoid divide-by-zero fault

[Biju Das]

Hi Hugo,

> -----Original Message-----
> From: Hugo Villeneuve <hugo@xxxxxxxxxxx>
> Sent: 08 April 2026 17:52
> Subject: Re: [PATCH v2 1/2] serial: sh-sci: Avoid divide-by-zero fault
> 
> Hi Biju,
> 
> On Wed, 8 Apr 2026 16:35:44 +0000
> Biju Das <biju.das.jz@xxxxxxxxxxxxxx> wrote:
> 
> > Hi Hugo,
> >
> > Thanks for the feedback.
> >
> > > -----Original Message-----
> > > From: Hugo Villeneuve <hugo@xxxxxxxxxxx>
> > > Sent: 08 April 2026 17:31
> > > Subject: Re: [PATCH v2 1/2] serial: sh-sci: Avoid divide-by-zero
> > > fault
> > >
> > > Hi Biju,
> > >
> > > On Wed,  8 Apr 2026 15:20:58 +0100
> > > Biju <biju.das.au@xxxxxxxxx> wrote:
> > >
> > > > From: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> > > >
> > > > uart_update_timeout() computes a timeout value by dividing by the
> > > > baud rate. If baud is zero — which can occur when the hardware
> > > > returns an unsupported or invalid rate — this results in a divide-by-zero fault.
> > >
> > > baud is returned by uart_get_baud_rate(), so this is not returned by the hardware?
> >
> > You are tight, Will update commit description.
> 
> How can uart_get_baud_rate() return a zero value? If I am not mistaken even for the B0 case, it will
> return 9600?

As per the comment and code, this API can return 0.

* If the new baud rate is invalid, try the @old termios setting. If it's still
* invalid, we try 9600 baud. If that is also invalid 0 is returned.

In drives/tty currently only 1 driver is checking the return value
and it calls panic

https://elixir.bootlin.com/linux/v7.0-rc7/source/drivers/tty/serial/apbuart.c#L214


I believe we should call panic, if baud =0, instead of proceeding.

Geert, any thoughts??

Cheers,
Biju