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>