This is a note to let you know that I've just added the patch titled
gpio: 74x164: Enable output pins after registers are reset
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
gpio-74x164-enable-output-pins-after-registers-are-r.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 99668eb1d801a65bb3d4c1d232308dec79a12cbb
Author: Arturas Moskvinas <arturas.moskvinas@xxxxxxxxx>
Date: Fri Mar 1 09:12:04 2024 +0200
gpio: 74x164: Enable output pins after registers are reset
[ 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@xxxxxxxxx>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/gpio/gpio-74x164.c b/drivers/gpio/gpio-74x164.c
index fb7b620763a25..a47897f2a83de 100644
--- a/drivers/gpio/gpio-74x164.c
+++ b/drivers/gpio/gpio-74x164.c
@@ -132,8 +132,6 @@ 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;
@@ -158,6 +156,8 @@ 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;
