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 <pho.tran@xxxxxxxxxx>
> ---
> 01/21/2021: Patch v3 modified based on comment from Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> 01/19/2021: Patch v2 Modified based on comment from Johan Hovold <johan@xxxxxxxxxx>
> and Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Giving credit in the commit log is nice, but this still doesn't say
anything about *what* you changed.
> ---
> 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
