USB: serial: cp210x: improve line-speed handling for CP2104 and CP2105

Quoted 10 lines · Johan Hovold

CP2104 and the ECI interface of CP2105 support further baud rates than the ones specified in AN205 table 1, and we can use the same equations as for CP2102N to determine and report back the actual baud rates used.

Note that this could eventually be generalised also to CP2108, which uses a different base clock. There appears to be an error in the CP2108 equations which needs to be confirmed on actual hardware first however (specifically, the subtraction of one from the divisor appears to be incorrect as it introduces larger errors).

Quoted 4 lines

Signed-off-by Johan Hovold <[email protected]>

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 drivers/usb/serial/cp210x.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

Reviewed-by Greg Kroah-Hartman <[email protected]>