On Thu, Feb 06, 2020 at 12:18:19PM +0100, Johan Hovold wrote:
> While assumed not to make a difference, not using the factor 2 prescaler
> makes the receiver more susceptible to errors.
>
> Specifically, there have been reports of problems with devices that
> cannot generate a 115200 rate with a smaller error than 2.1% (e.g.
> 117647 bps). But this can also be reproduced with a low-speed RS232
> tranceiver at 115200 when the input rate is close to nominal.
>
> So whenever possible, enable the factor 2 prescaler and halve the
> divisor in order to use settings closer to that of the previous
> algorithm.
>
> Fixes: 35714565089e ("USB: serial: ch341: reimplement line-speed handling")
> Cc: stable <stable@xxxxxxxxxxxxxxx> # 5.5
> Reported-by: Jakub Nantl <jn@xxxxxxxxxx>
> Tested-by: Jakub Nantl <jn@xxxxxxxxxx>
> Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
