| Message ID | 20230525040324.3773741-7-hugo@hugovil.com |
|---|---|
| State | New |
| Headers | show |
| Series | serial: sc16is7xx: fix GPIO regression and rs485 improvements | expand |
Thu, May 25, 2023 at 12:03:20AM -0400, Hugo Villeneuve kirjoitti: > From: Hugo Villeneuve <hvilleneuve@dimonoff.com> > > When we want to configure a pin as an output pin with a value of logic > 0, we end up as having a value of logic 1 on the output pin. Setting a > logic 0 a second time (or more) after that will correctly output a > logic 0 on the output pin. > > By default, all GPIO pins are configured as inputs. When we enter > c16is7xx_gpio_direction_output() for the first time, we first set the Missing 's'. > desired value in IOSTATE, and then we configure the pin as an output. > The datasheet states that writing to IOSTATE register will trigger a > transfer of the value to the I/O pin configured as output, so if the > pin is configured as an input, nothing will be transferred. > > Therefore, set the direction first in IODIR, and then set the desired > value in IOSTATE. > > This is what is done in NXP application note AN10587.
On Thu, 25 May 2023 14:10:27 +0300 andy.shevchenko@gmail.com wrote: > Thu, May 25, 2023 at 12:03:20AM -0400, Hugo Villeneuve kirjoitti: > > From: Hugo Villeneuve <hvilleneuve@dimonoff.com> > > > > When we want to configure a pin as an output pin with a value of logic > > 0, we end up as having a value of logic 1 on the output pin. Setting a > > logic 0 a second time (or more) after that will correctly output a > > logic 0 on the output pin. > > > > By default, all GPIO pins are configured as inputs. When we enter > > c16is7xx_gpio_direction_output() for the first time, we first set the > > Missing 's'. Fixed. > > desired value in IOSTATE, and then we configure the pin as an output. > > The datasheet states that writing to IOSTATE register will trigger a > > transfer of the value to the I/O pin configured as output, so if the > > pin is configured as an input, nothing will be transferred. > > > > Therefore, set the direction first in IODIR, and then set the desired > > value in IOSTATE. > > > > This is what is done in NXP application note AN10587. > > -- > With Best Regards, > Andy Shevchenko > > >
diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c index 8a2fc6f89d36..a5d8af0f6da0 100644 --- a/drivers/tty/serial/sc16is7xx.c +++ b/drivers/tty/serial/sc16is7xx.c @@ -1343,9 +1343,18 @@ static int sc16is7xx_gpio_direction_output(struct gpio_chip *chip, state |= BIT(offset); else state &= ~BIT(offset); - sc16is7xx_port_write(port, SC16IS7XX_IOSTATE_REG, state); + + /* + * If we write IOSTATE first, and then IODIR, the output value is not + * transferred to the corresponding I/O pin. + * The datasheet states that each register bit will be transferred to + * the corresponding I/O pin programmed as output when writing to + * IOSTATE. Therefore, configure direction first with IODIR, and then + * set value after with IOSTATE. + */ sc16is7xx_port_update(port, SC16IS7XX_IODIR_REG, BIT(offset), BIT(offset)); + sc16is7xx_port_write(port, SC16IS7XX_IOSTATE_REG, state); return 0; }