From 48533c0db74ccb0c7f2f53c9a9eb1c9ad2c33fd3 Mon Sep 17 00:00:00 2001 From: Hugo Villeneuve Date: Mon, 7 Aug 2023 17:45:55 -0400 Subject: [PATCH] serial: sc16is7xx: fix bug when first setting GPIO direction commit 9baeea723c0fb9c3ba9a336369f758ed9bc6831d upstream. When configuring 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 sc16is7xx_gpio_direction_output() for the first time, we first set the 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. Fixes: dfeae619d781 ("serial: sc16is7xx") Cc: stable@vger.kernel.org Signed-off-by: Hugo Villeneuve Reviewed-by: Lech Perczak Tested-by: Lech Perczak Link: https://lore.kernel.org/r/20230807214556.540627-6-hugo@hugovil.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/sc16is7xx.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c index ebea4a9d8e69..453cdcc9f322 100644 --- a/drivers/tty/serial/sc16is7xx.c +++ b/drivers/tty/serial/sc16is7xx.c @@ -1166,9 +1166,18 @@ 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; }