[PATCH 5.4 25/25] gpio: 74x164: Enable output pins after registers are reset

Greg Kroah-Hartman
2024-03-04T21:34:22Z

From: Arturas Moskvinas <arturas.moskvinas@gmail.com>

[ Upstream commit 530b1dbd97846b110ea8a94c7cc903eca21786e5 ]

Chip outputs are enabled[1] before actual reset is performed[2] which might
cause pin output value to flip flop if previous pin value was set to 1.
Fix that behavior by making sure chip is fully reset before all outputs are
enabled.

Flip-flop can be noticed when module is removed and inserted again and one of
the pins was changed to 1 before removal. 100 microsecond flipping is
noticeable on oscilloscope (100khz SPI bus).

For a properly reset chip - output is enabled around 100 microseconds (on 100khz
SPI bus) later during probing process hence should be irrelevant behavioral
change.

Fixes: 7ebc194d0fd4 (gpio: 74x164: Introduce 'enable-gpios' property)
Link: https://elixir.bootlin.com/linux/v6.7.4/source/drivers/gpio/gpio-74x164.c#L130 [1]
Link: https://elixir.bootlin.com/linux/v6.7.4/source/drivers/gpio/gpio-74x164.c#L150 [2]
Signed-off-by: Arturas Moskvinas <arturas.moskvinas@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpio/gpio-74x164.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpio-74x164.c b/drivers/gpio/gpio-74x164.c
index e81307f9754e3..30aa7f82fc5b4 100644
--- a/drivers/gpio/gpio-74x164.c
+++ b/drivers/gpio/gpio-74x164.c
@@ -128,8 +128,6 @@ static int gen_74x164_probe(struct spi_device *spi)
if (IS_ERR(chip->gpiod_oe))
return PTR_ERR(chip->gpiod_oe);

- gpiod_set_value_cansleep(chip->gpiod_oe, 1);
-
spi_set_drvdata(spi, chip);

chip->gpio_chip.label = spi->modalias;
@@ -154,6 +152,8 @@ static int gen_74x164_probe(struct spi_device *spi)
goto exit_destroy;
}

+ gpiod_set_value_cansleep(chip->gpiod_oe, 1);
+
ret = gpiochip_add_data(&chip->gpio_chip, chip);
if (!ret)
return 0;
--
2.43.0