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@vger.kernel.org # 5.5 Reported-by: Jakub Nantl jn@forever.cz Tested-by: Jakub Nantl jn@forever.cz Signed-off-by: Johan Hovold johan@kernel.org
Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org