The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 41ca302a697b64a3dab4676e01d0d11bb184737d Mon Sep 17 00:00:00 2001 From: Johan Hovold johan@kernel.org Date: Wed, 31 Aug 2022 10:15:25 +0200 Subject: [PATCH] USB: serial: ch341: fix disabled rx timer on older devices

At least one older CH341 appears to have the RX timer enable bit inverted so that setting it disables the RX timer and prevents the FIFO from emptying until it is full.

Only set the RX timer enable bit for devices with version newer than 0x27 (even though this probably affects all pre-0x30 devices).

Reported-by: Jonathan Woithe jwoithe@just42.net Tested-by: Jonathan Woithe jwoithe@just42.net Link: https://lore.kernel.org/r/Ys1iPTfiZRWj2gXs@marvin.atrad.com.au Fixes: 4e46c410e050 ("USB: serial: ch341: reinitialize chip on reconfiguration") Cc: stable@vger.kernel.org # 4.10 Signed-off-by: Johan Hovold johan@kernel.org

diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c index 2bcce172355b..af01a462cc43 100644 --- a/drivers/usb/serial/ch341.c +++ b/drivers/usb/serial/ch341.c @@ -253,8 +253,12 @@ static int ch341_set_baudrate_lcr(struct usb_device *dev, /* * CH341A buffers data until a full endpoint-size packet (32 bytes) * has been received unless bit 7 is set. + * + * At least one device with version 0x27 appears to have this bit + * inverted. */ - val |= BIT(7); + if (priv->version > 0x27) + val |= BIT(7);

r = ch341_control_out(dev, CH341_REQ_WRITE_REG, CH341_REG_DIVISOR << 8 | CH341_REG_PRESCALER,