Re: [PATCH v3 2/2] USB: serial: cp210x: Proper RTS control when buffers fill

[gregkh@xxxxxxxxxxxxxxxxxxx]

On Wed, Jun 24, 2020 at 07:03:04AM +0000, Phu Luu wrote:
> CP210x hardware disables auto-RTS but leaves auto-CTS when
> in hardware flow control mode and UART on cp210x hardware
> is disabled. This allows data to flow out, but new data
> will not come into the port. When re-opening the port, if
> auto-CTS is enabled on the cp210x, then auto-RTS must be
> re-enabled in the driver.
> 
> Signed-off-by: Phu Luu <phu.luu@xxxxxxxxxx>
> Signed-off-by: Brant Merryman <brant.merryman@xxxxxxxxxx>
> ---
> 06/09/2020: Patch v3 2/2 Modified based on feedback from Johan Hovold <johan@xxxxxxxxxx>
> 12/18/2019: Patch v2 Broken into two patches and modified based on feedback from Johan Hovold <johan@xxxxxxxxxx>
> 12/09/2019: Initial submission of patch "Proper RTS control when buffers fill"
> 
> drivers/usb/serial/cp210x.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> index bcceb4ad8be0..091441b1c5b9 100644
> --- a/drivers/usb/serial/cp210x.c
> +++ b/drivers/usb/serial/cp210x.c
> @@ -917,6 +917,7 @@ static void cp210x_get_termios_port(struct usb_serial_port *port,
>                u32 baud;
>                u16 bits;
>                u32 ctl_hs;
> +             u32 flow_repl;
>                 cp210x_read_u32_reg(port, CP210X_GET_BAUDRATE, &baud);
> @@ -1017,6 +1018,23 @@ static void cp210x_get_termios_port(struct usb_serial_port *port,
>                ctl_hs = le32_to_cpu(flow_ctl.ulControlHandshake);
>                if (ctl_hs & CP210X_SERIAL_CTS_HANDSHAKE) {
>                                dev_dbg(dev, "%s - flow control = CRTSCTS\n", __func__);
> +                             /*
> +                             * When the port is closed, the CP210x hardware disables
> +                             * auto-RTS and RTS is deasserted but it leaves auto-CTS when
> +                             * in hardware flow control mode. This prevents new data from
> +                             * being received by the port. When re-opening the port, if
> +                             * auto-CTS is enabled on the cp210x, then auto-RTS must be
> +                             * re-enabled in the driver.
> +                             */
> +                             flow_repl = le32_to_cpu(flow_ctl.ulFlowReplace);
> +                             flow_repl &= ~CP210X_SERIAL_RTS_MASK;
> +                             flow_repl |= CP210X_SERIAL_RTS_SHIFT(CP210X_SERIAL_RTS_FLOW_CTL);
> +                             flow_ctl.ulFlowReplace = cpu_to_le32(flow_repl);
> +                             cp210x_write_reg_block(port,
> +                                                             CP210X_SET_FLOW,
> +                                                             &flow_ctl,
> +                                                             sizeof(flow_ctl));
> +
>                                cflag |= CRTSCTS;
>                } else {
>                                dev_dbg(dev, "%s - flow control = NONE\n", __func__);
> --
> 2.17.0
> 

Hi,

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