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SubjectRe: [PATCH] tty/serial: at91: fix hardware handshake on Atmel platforms
Hi,

On 25/10/2016 at 18:11:35 +0200, Richard Genoud wrote :
> commit 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when
> hardware handshake is enabled"), despite its title, broke hardware
> handshake on *every* Atmel platforms.
>
> The only one partially working is the SAMA5D2.
>

[...]

> Changes since v4:
> - the mctrl_gpio_use_rtscts() is gone since it was atmel_serial
> specific. (so patch 1 is gone)
> - patches 2 and 3 have been merged together since it didn't make
> a lot of sense to correct the GPIO case in one separate patch.
> - ATMEL_US_USMODE_HWHS is now unset for platform with PDC
>
> Changes since v3:
> - remove superfluous #include <linux/err.h> (thanks to Uwe)
> - rebase on next-20160930
>
> Changes since v2:
> - remove IS_ERR_OR_NULL() test in patch 1/3 as Uwe suggested.
> - fix typos in patch 2/3
> - rebase on next-20160927
> - simplify the logic in patch 3/3.
>
> Changes since v1:
> - Correct patch 1 with the error found by kbuild.
> - Add Alexandre's Acked-by on patch 2
> - Rewrite patch 3 logic in the light of the on-going discussion
> with Cyrille and Alexandre.
>

The changelog has to go after the --- marker.

> * the list may not be exhaustive
>
> Signed-off-by: Richard Genoud <richard.genoud@gmail.com>

Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

> ---
> drivers/tty/serial/atmel_serial.c | 25 +++++++++++++++++++++----
> 1 file changed, 21 insertions(+), 4 deletions(-)
>
> I think this should go in the stable tree since it fixes the flow
> control broken since v4.0.
> But It won't compile on versions before 4.9rc1 because:
> function atmel_use_fifo was introduced in 4.4.12 / 4.7
> variable atmel_port was introduced in 4.9rc1
>
> That's why I didn't add the Cc stable in the email body.
>
>
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index fd8aa1f4ba78..2c7c45904ba7 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -2132,11 +2132,28 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
> mode |= ATMEL_US_USMODE_RS485;
> } else if (termios->c_cflag & CRTSCTS) {
> /* RS232 with hardware handshake (RTS/CTS) */
> - if (atmel_use_dma_rx(port) && !atmel_use_fifo(port)) {
> - dev_info(port->dev, "not enabling hardware flow control because DMA is used");
> - termios->c_cflag &= ~CRTSCTS;
> - } else {
> + if (atmel_use_fifo(port) &&
> + !mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_CTS)) {
> + /*
> + * with ATMEL_US_USMODE_HWHS set, the controller will
> + * be able to drive the RTS pin high/low when the RX
> + * FIFO is above RXFTHRES/below RXFTHRES2.
> + * It will also disable the transmitter when the CTS
> + * pin is high.
> + * This mode is not activated if CTS pin is a GPIO
> + * because in this case, the transmitter is always
> + * disabled.
> + * If the RTS pin is a GPIO, the controller won't be
> + * able to drive it according to the FIFO thresholds,
> + * but it will be handled by the driver.
> + */
> mode |= ATMEL_US_USMODE_HWHS;
> + } else {
> + /*
> + * For platforms without FIFO, the flow control is
> + * handled by the driver.
> + */
> + mode |= ATMEL_US_USMODE_NORMAL;
> }
> } else {
> /* RS232 without hadware handshake */

--
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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