Re: [PATCH v4] USB: serial: cp210x: Fix error 32 when hardware flow control is enabled.
From: Johan Hovold <johan@kernel.org>
Date: 2021-01-25 13:50:20
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On Thu, Jan 21, 2021 at 09:52:23AM +0000, Pho Tran wrote:
Fix error 32 returned by CP210X_SET_MHS when hardware flow control is enabled. The root cause of error 32 is that user application (CoolTerm, linux-serial-test) opened cp210x device with hardware flow control then attempt to control RTS/DTR pins. In hardware flow control, RTS/DTR pins will be controlled by hardware only, any attempt to control those pins will cause error 32 from the device. This fix will block MHS command(command to control RTS/DTR pins) to the device if hardware flow control is being used. Signed-off-by: Pho Tran <redacted> --- 01/21/2021: Patch v3 modified based on comment from Greg Kroah-Hartman [off-list ref] 01/19/2021: Patch v2 Modified based on comment from Johan Hovold [off-list ref] and Greg Kroah-Hartman [off-list ref]
Giving credit in the commit log is nice, but this still doesn't say anything about *what* you changed.
quoted hunk ↗ jump to hunk
--- drivers/usb/serial/cp210x.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c index fbb10dfc56e3..814dff5fee98 100644 --- a/drivers/usb/serial/cp210x.c +++ b/drivers/usb/serial/cp210x.c@@ -1204,7 +1204,12 @@ static int cp210x_tiocmset(struct tty_struct *tty, unsigned int set, unsigned int clear) { struct usb_serial_port *port = tty->driver_data; - return cp210x_tiocmset_port(port, set, clear); + + /* Don't send SET_MHS command if device in hardware flow control mode. */ + if (C_CRTSCTS(tty)) + return 0;
You didn't reply to my comments that what should be done here is to disable auto-RTS when clearing TIOCM_RST and re-enable it when setting the same bit. If you disagree with review feedback you need to say so and not just resend a new version of your patch without an explanation. Note that the above would also needlessly prevent DTR from being changed whenever auto-RTS is enabled and return success instead of an error to user space. My suggestion for how to suppress the error message from dtr_rts() suffers from the same problem so I've updated that patch and implemented proper RTS handling in the driver now. This takes care not only of the SET_MHS error messages, but also makes sure that RTS can always be deasserted and some other related issues with regards to modem control.
+ else + return cp210x_tiocmset_port(port, set, clear); } static int cp210x_tiocmset_port(struct usb_serial_port *port,
Johan