Re: [PATCH 2/2] serial: sc16is7xx: setup reset pin if it is defined in device tree

[Hui Wang <hui.wang@xxxxxxxxxxxxx>]

Hi Hugo,

Will address all your comment in the v2.

Thanks,

Hui.

On 6/3/24 21:11, Hugo Villeneuve wrote:
> On Mon,  3 Jun 2024 20:37:10 +0800
> Hui Wang <hui.wang@xxxxxxxxxxxxx> wrote:
>
> Hi Hui,
>
> > Certain designs connect a gpio to the reset pin, and the reset pin
> > needs to be setup correctly before accessing the chip.
> >
> > Here adding a function to handle the reset pin. This change has no
> > impact if there is no reset_gpios defined in the device tree.
> >
> > Signed-off-by: Hui Wang <hui.wang@xxxxxxxxxxxxx>
> > ---
> >   drivers/tty/serial/sc16is7xx.c     | 22 ++++++++++++++++++++++
> >   drivers/tty/serial/sc16is7xx.h     |  2 ++
> >   drivers/tty/serial/sc16is7xx_i2c.c |  2 ++
> >   drivers/tty/serial/sc16is7xx_spi.c |  2 ++
> >   4 files changed, 28 insertions(+)
> >
> > diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
> > index bf0065d1c8e9..53bfb603b03c 100644
> > --- a/drivers/tty/serial/sc16is7xx.c
> > +++ b/drivers/tty/serial/sc16is7xx.c
> > @@ -19,6 +19,7 @@
> >   #include <linux/kthread.h>
> >   #include <linux/mod_devicetable.h>
> >   #include <linux/module.h>
> > +#include <linux/of_gpio.h>
> >   #include <linux/property.h>
> >   #include <linux/regmap.h>
> >   #include <linux/sched.h>
> > @@ -1467,6 +1468,27 @@ static const struct serial_rs485 sc16is7xx_rs485_supported = {
> >   	.delay_rts_after_send = 1,	/* Not supported but keep returning -EINVAL */
> >   };
> >   
> > +void sc16is7xx_setup_reset_pin(struct device *dev)
> Potentially rename to sc16is7xx_reset() based on my comments below
> about software reset.
>
> > +{
> > +	struct device_node *np = dev->of_node;
> > +	int reset_gpio, err;
> > +
> > +	reset_gpio = of_get_named_gpio(np, "reset-gpios", 0);
> Maybe use devm_gpiod_get_optional() to simplify and avoid OF-specific
> code.
>
> > +	if (!gpio_is_valid(reset_gpio))
> > +		return;
> > +
> > +	err = devm_gpio_request_one(dev, reset_gpio, GPIOF_OUT_INIT_LOW,
> > +				    "sc16is7xx-reset");
> > +	if (err) {
> > +		dev_err(dev, "failed to request sc16is7xx-reset-gpios: %d\n", err);
> > +		return;
> When this error happens, you return no error to the calling function,
> why? If you specify a reset GPIO in your device tree, and you cannot use
> it, seems like an error worth reporting.
>
> > +	}
> > +
> > +	/* Deassert the reset pin */
> Do you respect the manufacturer's minimum reset pulse width? The
> datasheet states that its 3 us, so maybe add a delay before deassertion.
>
> > +	gpio_set_value_cansleep(reset_gpio, 1);
> > +}
> > +EXPORT_SYMBOL_GPL(sc16is7xx_setup_reset_pin);
> > +
> >   int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
> >   		    struct regmap *regmaps[], int irq)
> >   {
> > diff --git a/drivers/tty/serial/sc16is7xx.h b/drivers/tty/serial/sc16is7xx.h
> > index afb784eaee45..f4ae114cc41a 100644
> > --- a/drivers/tty/serial/sc16is7xx.h
> > +++ b/drivers/tty/serial/sc16is7xx.h
> > @@ -33,6 +33,8 @@ const char *sc16is7xx_regmap_name(u8 port_id);
> >   
> >   unsigned int sc16is7xx_regmap_port_mask(unsigned int port_id);
> >   
> > +void sc16is7xx_setup_reset_pin(struct device *dev);
> > +
> >   int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
> >   		    struct regmap *regmaps[], int irq);
> >   
> > diff --git a/drivers/tty/serial/sc16is7xx_i2c.c b/drivers/tty/serial/sc16is7xx_i2c.c
> > index 3ed47c306d85..9833c3b935c2 100644
> > --- a/drivers/tty/serial/sc16is7xx_i2c.c
> > +++ b/drivers/tty/serial/sc16is7xx_i2c.c
> > @@ -21,6 +21,8 @@ static int sc16is7xx_i2c_probe(struct i2c_client *i2c)
> >   	if (!devtype)
> >   		return dev_err_probe(&i2c->dev, -ENODEV, "Failed to match device\n");
> >   
> > +	sc16is7xx_setup_reset_pin(&i2c->dev);
> Move this call inside sc16is7xx_probe() function, since it is common to
> both i2c and spi interfaces. Also, you will see in sc16is7xx_probe()
> that we already issue a software reset. If you
> specify a hardware reset pin, then you shouldn't issue the software
> reset.
>
> > +
> >   	memcpy(&regcfg, &sc16is7xx_regcfg, sizeof(struct regmap_config));
> >   
> >   	for (i = 0; i < devtype->nr_uart; i++) {
> > diff --git a/drivers/tty/serial/sc16is7xx_spi.c b/drivers/tty/serial/sc16is7xx_spi.c
> > index 73df36f8a7fd..ce38561faaf0 100644
> > --- a/drivers/tty/serial/sc16is7xx_spi.c
> > +++ b/drivers/tty/serial/sc16is7xx_spi.c
> > @@ -38,6 +38,8 @@ static int sc16is7xx_spi_probe(struct spi_device *spi)
> >   	if (!devtype)
> >   		return dev_err_probe(&spi->dev, -ENODEV, "Failed to match device\n");
> >   
> > +	sc16is7xx_setup_reset_pin(&spi->dev);
> > +
> >   	memcpy(&regcfg, &sc16is7xx_regcfg, sizeof(struct regmap_config));
> >   
> >   	for (i = 0; i < devtype->nr_uart; i++) {
> > --
> > 2.34.1