A subset of CH341 devices does not support all features, namely the prescaler is limited to a reduced precision and there is no support for sending a RS232 break condition. These devices can usually be identified by an imprint of "340" on the turquoise-colored plug. They're also sometimes called "HL340", but not all such devices are affected. This series takes multiple steps to support the limited chips: * Remove special cases from clock prescaler computation * Detect limited devices by trying to read a register related to sending a break condition * Amend clock prescaler computation to only use working values on limited chips * Simulate an RS232 break condition by temporarily lowering the baud rate and sending a NUL byte Michael Hanselmann (6): USB: serial: ch341: Reduce special cases in clock calculation USB: serial: ch341: Add basis for quirk detection USB: serial: ch341: Limit prescaler on quirky chips USB: serial: ch341: Name prescaler, divisor registers USB: serial: ch341: Compute minimum baud rate USB: serial: ch341: Simulate break condition if not supported drivers/usb/serial/ch341.c | 294 ++++++++++++++++++++++++++++++------- 1 file changed, 244 insertions(+), 50 deletions(-) -- 2.20.1
