Re: [PATCH] ARM/serial: at91: switch atmel serial to use gpiolib

[Nicolas Ferre <nicolas.ferre@atmel.com>]

On 05/11/2013 13:35, Linus Walleij :
> This passes the errata fix using a GPIO to control the RTS pin
> on one of the AT91 chips to use gpiolib instead of the
> AT91-specific interfaces. Also remove the reliance on
> compile-time #defines and the cpu_* check and rely on the
> platform passing down the proper GPIO pin through platform
> data.
>
> This is a prerequisite for getting rid of the local GPIO
> implementation in the AT91 platform and move toward
> multiplatform.
>
> This also makes way for device tree conversion: the RTS
> GPIO pin can be passed by standard GPIO bindings.
>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> This is an alternative to the patch entitled
> "ARM/serial: at91: move machine quirk into machine"
> which needs testing to confirm this approach.
> Seeking ACKs on this if the approach seems OK to
> all parties.
> ---
>   arch/arm/mach-at91/at91rm9200_devices.c |  1 +
>   drivers/tty/serial/atmel_serial.c       | 51 +++++++++++++++++++++------------
>   include/linux/platform_data/atmel.h     |  1 +
>   3 files changed, 35 insertions(+), 18 deletions(-)
>
> diff --git a/arch/arm/mach-at91/at91rm9200_devices.c b/arch/arm/mach-at91/at91rm9200_devices.c
> index c721e9b08066..51d4c08962f6 100644
> --- a/arch/arm/mach-at91/at91rm9200_devices.c
> +++ b/arch/arm/mach-at91/at91rm9200_devices.c
> @@ -961,6 +961,7 @@ static struct resource uart0_resources[] = {
>   static struct atmel_uart_data uart0_data = {
>   	.use_dma_tx	= 1,
>   	.use_dma_rx	= 1,
> +	.rts_gpio	= AT91_PIN_PA21,
>   };
>
>   static u64 uart0_dmamask = DMA_BIT_MASK(32);
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index d067285a2d20..3d5c848cdfe1 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -41,15 +41,11 @@
>   #include <linux/uaccess.h>
>   #include <linux/platform_data/atmel.h>
>   #include <linux/timer.h>
> +#include <linux/gpio.h>
>
>   #include <asm/io.h>
>   #include <asm/ioctls.h>
>
> -#ifdef CONFIG_ARM
> -#include <mach/cpu.h>
> -#include <asm/gpio.h>
> -#endif
> -
>   #define PDC_BUFFER_SIZE		512
>   /* Revisit: We should calculate this based on the actual port settings */
>   #define PDC_RX_TIMEOUT		(3 * 10)		/* 3 bytes */
> @@ -167,6 +163,7 @@ struct atmel_uart_port {
>   	struct circ_buf		rx_ring;
>
>   	struct serial_rs485	rs485;		/* rs485 settings */
> +	int			rts_gpio;	/* optional RTS GPIO */
>   	unsigned int		tx_done_mask;
>   	bool			is_usart;	/* usart or uart */
>   	struct timer_list	uart_timer;	/* uart timer */
> @@ -300,20 +297,17 @@ static void atmel_set_mctrl(struct uart_port *port, u_int mctrl)
>   	unsigned int mode;
>   	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
>
> -#ifdef CONFIG_ARCH_AT91RM9200
> -	if (cpu_is_at91rm9200()) {
> -		/*
> -		 * AT91RM9200 Errata #39: RTS0 is not internally connected
> -		 * to PA21. We need to drive the pin manually.
> -		 */
> -		if (port->mapbase == AT91RM9200_BASE_US0) {
> -			if (mctrl & TIOCM_RTS)
> -				at91_set_gpio_value(AT91_PIN_PA21, 0);
> -			else
> -				at91_set_gpio_value(AT91_PIN_PA21, 1);
> -		}
> +	/*
> +	 * AT91RM9200 Errata #39: RTS0 is not internally connected
> +	 * to PA21. We need to drive the pin as a GPIO.
> +	 */
> +	if (gpio_is_valid(atmel_port->rts_gpio) &&
> +	    port->mapbase == AT91RM9200_BASE_US0) {

Okay. Let's keep it like this for the moment. If I want to generalize 
this "feature" to other SoCs, I will remove the second test.


> +		if (mctrl & TIOCM_RTS)
> +			gpio_set_value(atmel_port->rts_gpio, 0);
> +		else
> +			gpio_set_value(atmel_port->rts_gpio, 1);
>   	}
> -#endif
>
>   	if (mctrl & TIOCM_RTS)
>   		control |= ATMEL_US_RTSEN;
> @@ -2365,6 +2359,27 @@ static int atmel_serial_probe(struct platform_device *pdev)
>   	port = &atmel_ports[ret];
>   	port->backup_imr = 0;
>   	port->uart.line = ret;
> +	port->rts_gpio = -1; /* Invalid, zero could be valid */

What about -EINVAL?

> +	/*
> +	 * In theory the GPIO pin controlling RTS could be zero and
> +	 * this would be an improper check, but we know that the only
> +	 * existing case is != 0 and it's nice to use the zero-initialized
> +	 * structs to indicate "no RTS GPIO" instead of open-coding some
> +	 * invalid value everywhere.
> +	 */
> +	if (pdata->rts_gpio > 0) {

Okay, let's do the gpio validity checking like this. It is preventing us 
from big headache.

But, unfortunately, on DT-enabled machines we do not have a pdata 
structure. You would have to change the test to:

+	if (pdata && pdata->rts_gpio > 0) {

But anyway, I send an DT support for this feature as a follow-up of this 
patch. You can squash both patches if you want.

> +		ret = devm_gpio_request(&pdev->dev, pdata->rts_gpio, "RTS");
> +		if (ret) {
> +			dev_err(&pdev->dev, "error requesting RTS GPIO\n");
> +			goto err;
> +		}
> +		port->rts_gpio = pdata->rts_gpio;
> +		ret = gpio_direction_output(port->rts_gpio, 0);
> +		if (ret) {
> +			dev_err(&pdev->dev, "error setting up RTS GPIO\n");
> +			goto err;
> +		}
> +	}
>
>   	ret = atmel_init_port(port, pdev);
>   	if (ret)
> diff --git a/include/linux/platform_data/atmel.h b/include/linux/platform_data/atmel.h
> index cea9f70133c5..e26b0c14edea 100644
> --- a/include/linux/platform_data/atmel.h
> +++ b/include/linux/platform_data/atmel.h
> @@ -84,6 +84,7 @@ struct atmel_uart_data {
>   	short			use_dma_rx;	/* use receive DMA? */
>   	void __iomem		*regs;		/* virt. base address, if any */
>   	struct serial_rs485	rs485;		/* rs485 settings */
> +	int			rts_gpio;	/* optional RTS GPIO */
>   };
>
>    /* Touchscreen Controller */
>


-- 
Nicolas Ferre