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kernel: backport gpio emulated open drain output fix

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Backport the GPIO emulated open drain output fix from v5.5, which is
required for the i2c-pxa backport.

Signed-off-by: Russell King <linux@armlinux.org.uk>
This commit is contained in:
Russell King 2020-05-21 09:57:22 +01:00 committed by Petr Štetiar
parent 017320ead3
commit 72a1d5c3ac
1 changed files with 45 additions and 0 deletions
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45
target/linux/generic/backport-5.4/802-v5.5-gpiolib-fix-up-emulated-open-drain-outputs.patch Normal file
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@ -0,0 +1,45 @@
From: Russell King <rmk+kernel@armlinux.org.uk>
Bcc: linux@mail.armlinux.org.uk
Cc: Linus Walleij <linus.walleij@linaro.org>,Bartosz Golaszewski <bgolaszewski@baylibre.com>,linux-gpio@vger.kernel.org
Subject: [PATCH] gpiolib: fix up emulated open drain outputs
MIME-Version: 1.0
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
Content-Type: text/plain; charset="utf-8"
gpiolib has a corner case with open drain outputs that are emulated.
When such outputs are outputting a logic 1, emulation will set the
hardware to input mode, which will cause gpiod_get_direction() to
report that it is in input mode. This is different from the behaviour
with a true open-drain output.
Unify the semantics here.
Suggested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
drivers/gpio/gpiolib.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 104ed299d5ea..99d19f80440e 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -220,6 +220,14 @@ int gpiod_get_direction(struct gpio_desc *desc)
chip = gpiod_to_chip(desc);
offset = gpio_chip_hwgpio(desc);
+ /*
+ * Open drain emulation using input mode may incorrectly report
+ * input here, fix that up.
+ */
+ if (test_bit(FLAG_OPEN_DRAIN, &desc->flags) &&
+ test_bit(FLAG_IS_OUT, &desc->flags))
+ return 0;
+
if (!chip->get_direction)
return -ENOTSUPP;
--
2.20.1