Subject: [PATCH v4 2/4] serial: mxs-auart: use mctrl_gpio helpers for handling modem signals

From: [email-masked] (Richard Genoud)
Date: Fri, 24 Oct 2014 17:32:06 +0200

On 10/10/2014 18:53, Janusz Uzycki wrote:
> Dedicated CTS and RTS pins are unusable together with a lot of other
> peripherals because they share the same line. Pinctrl is limited.
> 
> Moreover, the AUART controller doesn't handle DTR/DSR/DCD/RI signals,
> so we have to control them via GPIO.
> 
> This patch permits to use GPIOs to control the CTS/RTS/DTR/DSR/DCD/RI
> signals.
> 
> Signed-off-by: Janusz Uzycki <[email-masked]>
> ---
> v3 -> v4 changelog:
> * RTS_AT_AUART() and CTS_AT_AUART() macro defined
> * DMA engine disabled if RTS or CTS is GPIO line
> * warn if fsl,uart-has-rtscts and RTS/CTS via GPIO are mixed
> * CTSEN can't be enabled for hardware flow control block
>   if CTS is defined as GPIO line
> * RTSEN can be enabled for hardware flow control block
>   even if RTS is defined as GPIO line.
>   RTS pin depends on pinctrl configuration which
>   selects RTS output from hardware flow control block or GPIO line.
> * mxs_auart_settermios(): RTS_AT_AUART() and CTS_AT_AUART() used
> * mxs_auart_irq_handle(): CTS_AT_AUART() used
> * mxs_auart_init_gpios() returns true(success)/false(failure)
> * dev_err() message fixed in mxs_auart_probe()
> 
> v2 -> v3 changelog:
> * mctrl_gpio_free() removed to simplify:
>   mctrl_gpio_free() is not necessary in mxs_auart_probe() and
>   mxs_auart_remove() because mctrl_gpio_init() does all
>   allocations with devm_* functions.
>   (see Documentation/serial/driver since kernel 3.16)
> * DMA on HW flow control comment updated, still not sure about the comment
> * mxs_auart_modem_status() removed from mxs_auart_get_mctrl():
>   mctrl_gpio_get() does not clear gpio interrupt pendings like
>   8250_core.c does with MSR.
> * mxs_auart_modem_status() moved to [3/4]
>   If enable_ms() is not called, uart_handle_cts_change()
>   shouldn't be called.
> 
> ---
>  .../devicetree/bindings/serial/fsl-mxs-auart.txt   | 10 ++++-
>  drivers/tty/serial/Kconfig           |  1 +
>  drivers/tty/serial/mxs-auart.c       | 50 +++++++++++++++++++---
>  3 files changed, 55 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/serial/fsl-mxs-auart.txt b/Documentation/devicetree/bindings/serial/fsl-mxs-auart.txt
> index 59a40f1..7c408c8 100644
> --- a/Documentation/devicetree/bindings/serial/fsl-mxs-auart.txt
> +++ b/Documentation/devicetree/bindings/serial/fsl-mxs-auart.txt
> @@ -11,8 +11,13 @@ Required properties:
>  - dma-names: "rx" for RX channel, "tx" for TX channel.
>  
>  Optional properties:
> -- fsl,uart-has-rtscts : Indicate the UART has RTS and CTS lines,
> +- fsl,uart-has-rtscts : Indicate the UART has RTS and CTS lines
> +  for hardware flow control,
>  	it also means you enable the DMA support for this UART.
> +- {rts,cts,dtr,dsr,rng,dcd}-gpios: specify a GPIO for RTS/CTS/DTR/DSR/RI/DCD
> +  line respectively. It will use specified PIO instead of the peripheral
> +  function pin for the USART feature.
> +  If unsure, don't specify this property.
>  
>  Example:
>  auart0: serial at 8006a000 {
> @@ -21,6 +26,9 @@ auart0: serial at 8006a000 {
>  	interrupts = <112>;
>  	dmas = <&dma_apbx 8>, <&dma_apbx 9>;
>  	dma-names = "rx", "tx";
> +	cts-gpios = <&gpio1 15 GPIO_ACTIVE_LOW>;
> +	dsr-gpios = <&gpio1 16 GPIO_ACTIVE_LOW>;
> +	dcd-gpios = <&gpio1 17 GPIO_ACTIVE_LOW>;
>  };
>  
>  Note: Each auart port should have an alias correctly numbered in "aliases"
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index 4fe8ca1..90e8516 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -1357,6 +1357,7 @@ config SERIAL_MXS_AUART
>  	depends on ARCH_MXS
>  	tristate "MXS AUART support"
>  	select SERIAL_CORE
> +	select SERIAL_MCTRL_GPIO if GPIOLIB
>  	help
>  	  This driver supports the MXS Application UART (AUART) port.
>  
> diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
> index 2d49901..8bbcfd1 100644
> --- a/drivers/tty/serial/mxs-auart.c
> +++ b/drivers/tty/serial/mxs-auart.c
> @@ -42,6 +42,9 @@
>  
>  #include <asm/cacheflush.h>
>  
> +#include <linux/err.h>
> +#include "serial_mctrl_gpio.h"
> +
>  #define MXS_AUART_PORTS 5
>  #define MXS_AUART_FIFO_SIZE		16
>  
> @@ -158,6 +161,8 @@ struct mxs_auart_port {
>  	struct scatterlist rx_sgl;
>  	struct dma_chan	*rx_dma_chan;
>  	void *rx_dma_buf;
> +
> +	struct mctrl_gpios	*gpios;
>  };
>  
>  static struct platform_device_id mxs_auart_devtype[] = {
> @@ -405,6 +410,8 @@ static void mxs_auart_release_port(struct uart_port *u)
>  
>  static void mxs_auart_set_mctrl(struct uart_port *u, unsigned mctrl)
>  {
> +	struct mxs_auart_port *s = to_auart_port(u);
> +
>  	u32 ctrl = readl(u->membase + AUART_CTRL2);
>  
>  	ctrl &= ~(AUART_CTRL2_RTSEN | AUART_CTRL2_RTS);
> @@ -416,17 +423,20 @@ static void mxs_auart_set_mctrl(struct uart_port *u, unsigned mctrl)
>  	}
>  
>  	writel(ctrl, u->membase + AUART_CTRL2);
> +
> +	mctrl_gpio_set(s->gpios, mctrl);
>  }
>  
>  static u32 mxs_auart_get_mctrl(struct uart_port *u)
>  {
> +	struct mxs_auart_port *s = to_auart_port(u);
>  	u32 stat = readl(u->membase + AUART_STAT);
>  	u32 mctrl = 0;
>  
>  	if (stat & AUART_STAT_CTS)
>  		mctrl |= TIOCM_CTS;
>  
> -	return mctrl;
> +	return mctrl_gpio_get(s->gpios, &mctrl);
>  }
>  
>  static int mxs_auart_dma_prep_rx(struct mxs_auart_port *s);
> @@ -554,6 +564,10 @@ err_out:
>  
>  }
>  
> +#define RTS_AT_AUART()	IS_ERR_OR_NULL(mctrl_gpio_to_gpiod(s->gpios,	\
> +							UART_GPIO_RTS))
> +#define CTS_AT_AUART()	IS_ERR_OR_NULL(mctrl_gpio_to_gpiod(s->gpios,	\
> +							UART_GPIO_CTS))
>  static void mxs_auart_settermios(struct uart_port *u,
>  				 struct ktermios *termios,
>  				 struct ktermios *old)
> @@ -630,6 +644,7 @@ static void mxs_auart_settermios(struct uart_port *u,
>  		ctrl |= AUART_LINECTRL_STP2;
>  
>  	/* figure out the hardware flow control settings */
> +	ctrl2 &= ~(AUART_CTRL2_CTSEN | AUART_CTRL2_RTSEN);
>  	if (cflag & CRTSCTS) {
>  		/*
>  		 * The DMA has a bug(see errata:2836) in mx23.
> @@ -644,9 +659,11 @@ static void mxs_auart_settermios(struct uart_port *u,
>  				ctrl2 |= AUART_CTRL2_TXDMAE | AUART_CTRL2_RXDMAE
>  				       | AUART_CTRL2_DMAONERR;
>  		}
> -		ctrl2 |= AUART_CTRL2_CTSEN | AUART_CTRL2_RTSEN;
> -	} else {
> -		ctrl2 &= ~(AUART_CTRL2_CTSEN | AUART_CTRL2_RTSEN);
> +		/* Even if RTS is GPIO line RTSEN can be enabled because
> +		 * the pinctrl configuration decides about RTS pin function */
> +		ctrl2 |= AUART_CTRL2_RTSEN;
> +		if (CTS_AT_AUART())
> +			ctrl2 |= AUART_CTRL2_CTSEN;
>  	}
>  
>  	/* set baud rate */
> @@ -690,7 +707,9 @@ static irqreturn_t mxs_auart_irq_handle(int irq, void *context)
>  			s->port.membase + AUART_INTR_CLR);
>  
>  	if (istat & AUART_INTR_CTSMIS) {
> -		uart_handle_cts_change(&s->port, stat & AUART_STAT_CTS);
> +		if (CTS_AT_AUART())
> +			uart_handle_cts_change(&s->port,
> +					stat & AUART_STAT_CTS);
>  		writel(AUART_INTR_CTSMIS,
>  				s->port.membase + AUART_INTR_CLR);
>  		istat &= ~AUART_INTR_CTSMIS;
> @@ -1014,6 +1033,23 @@ static int serial_mxs_probe_dt(struct mxs_auart_port *s,
>  	return 0;
>  }
>  
> +static bool mxs_auart_init_gpios(struct mxs_auart_port *s, struct device *dev)
> +{
> +	s->gpios = mctrl_gpio_init(dev, 0);
> +	if (IS_ERR_OR_NULL(s->gpios))
> +		return false;
> +
> +	/* Block (enabled before) DMA option if RTS or CTS is GPIO line */
This is confusing, so I think some more comments won't be too much.
Something like:
/*
 * The DMA only work if the lines CTS/RTS are handled by the controller
 * cf. 8418e67d9523 serial: mxs: enable the DMA only when the RTS/CTS is
valid
 * So, If the CTS/RTS lines are controlled via GPIO the MXS_AUART_RTSCTS
bit should be
 * cleaned to indicate that the RTS/CTS lines are not handled by the
controller.
 */
(If I understood correctly what is done here.)
> +	if (!RTS_AT_AUART() || !CTS_AT_AUART()) {
> +		if (test_bit(MXS_AUART_RTSCTS, &s->flags))
> +			dev_warn(dev,
> +				 "DMA and flow control via gpio may cause some problems. DMA disabled!\n");
> +		clear_bit(MXS_AUART_RTSCTS, &s->flags);
> +	}
> +
> +	return true;
> +}
> +
>  static int mxs_auart_probe(struct platform_device *pdev)
>  {
>  	const struct of_device_id *of_id =
> @@ -1069,6 +1105,10 @@ static int mxs_auart_probe(struct platform_device *pdev)
>  
>  	platform_set_drvdata(pdev, s);
>  
> +	if (!mxs_auart_init_gpios(s, &pdev->dev))
> +		dev_err(&pdev->dev,
> +			"Failed to initialize GPIOs. The serial port may not work as expected\n");
> +
>  	auart_port[s->port.line] = s;
>  
>  	mxs_auart_reset(&s->port);
> 
Reviewed-by: Richard Genoud <[email-masked]>