Re: [PATCH] serial: atmel: fix incorrect baudrate setup

[Tobias Schramm]

Am 09.01.23 um 08:07 schrieb Greg Kroah-Hartman:
> On Mon, Jan 09, 2023 at 08:02:00AM +0100, Tobias Schramm wrote:
> > Commit ba47f97a18f2 ("serial: core: remove baud_rates when serial console
> > setup") changed uart_set_options to select the correct baudrate
> > configuration based on the absolute error between requested baudrate and
> > available standard baudrate settings.
> > Prior to that commit the baudrate was selected based on which predefined
> > standard baudrate did not exceed the requested baudrate.
> > This change of selection logic was never reflected in the atmel serial
> > driver. Thus the comment left in the atmel serial driver is no longer
> > accurate.
> > Additionally the manual rounding up described in that comment and applied
> > via (quot - 1) requests an incorrect baudrate. Since uart_set_options uses
> > tty_termios_encode_baud_rate to determine the appropriate baudrate flags
> > this can cause baudrate selection to fail entirely because
> > tty_termios_encode_baud_rate will only select a baudrate if relative error
> > between requested and selected baudrate does not exceed +/-2%.
> > Fix that by requesting actual, exact baudrate used by the serial.
> >
> > Signed-off-by: Tobias Schramm <t.schramm@xxxxxxxxxxx>
> > ---
> What commit id does this fix?  Please list that as a the "Fixes:" tag.

Commit ba47f97a18f2 ("serial: core: remove baud_rates when serial console
setup") is the one that breaks the assumptions made in the driver.
I'll send a v2 and include that.

> Also, does this need to go to older/stable kernels?
Yep,  this should go to older kernels as a fix, too.
> thanks,
>
> greg k-h