openwrt/target/linux/brcm2708/patches-4.19/950-0700-regulator-gpio-Allow-nonexclusive-GPIO-access.patch

From f6d983b7bc9ae79d0eb4dea7bc30a1ad5ff428a7 Mon Sep 17 00:00:00 2001
From: Linus Walleij <linus.walleij@linaro.org>
Date: Fri, 12 Oct 2018 14:54:12 +0200
Subject: [PATCH] regulator/gpio: Allow nonexclusive GPIO access

commit b0ce7b29bfcd090ddba476f45a75ec0a797b048a upstream.

[ This is a partial cherry-pick, omitting the regulator
change which isn't required ]

This allows nonexclusive (simultaneous) access to a single
GPIO line for the fixed regulator enable line. This happens
when several regulators use the same GPIO for enabling and
disabling a regulator, and all need a handle on their GPIO
descriptor.

This solution with a special flag is not entirely elegant
and should ideally be replaced by something more careful as
this makes it possible for several consumers to
enable/disable the same GPIO line to the left and right
without any consistency. The current use inside the regulator
core should however be fine as it takes special care to
handle this.

For the state of the GPIO backend, this is still the
lesser evil compared to going back to global GPIO
numbers.

Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Jon Hunter <jonathanh@nvidia.com>
Fixes: efdfeb079cc3 ("regulator: fixed: Convert to use GPIO descriptor only")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 drivers/gpio/gpiolib.c        | 19 +++++++++++++++++--
 include/linux/gpio/consumer.h |  1 +
 2 files changed, 18 insertions(+), 2 deletions(-)

--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3979,8 +3979,23 @@ struct gpio_desc *__must_check gpiod_get
 	 * the device name as label
 	 */
 	status = gpiod_request(desc, con_id ? con_id : devname);
-	if (status < 0)
-		return ERR_PTR(status);
+	if (status < 0) {
+		if (status == -EBUSY && flags & GPIOD_FLAGS_BIT_NONEXCLUSIVE) {
+			/*
+			 * This happens when there are several consumers for
+			 * the same GPIO line: we just return here without
+			 * further initialization. It is a bit if a hack.
+			 * This is necessary to support fixed regulators.
+			 *
+			 * FIXME: Make this more sane and safe.
+			 */
+			dev_info(dev, "nonexclusive access to GPIO for %s\n",
+				 con_id ? con_id : devname);
+			return desc;
+		} else {
+			return ERR_PTR(status);
+		}
+	}
 
 	status = gpiod_configure_flags(desc, con_id, lookupflags, flags);
 	if (status < 0) {
--- a/include/linux/gpio/consumer.h
+++ b/include/linux/gpio/consumer.h
@@ -30,6 +30,7 @@ struct gpio_descs {
 #define GPIOD_FLAGS_BIT_DIR_OUT		BIT(1)
 #define GPIOD_FLAGS_BIT_DIR_VAL		BIT(2)
 #define GPIOD_FLAGS_BIT_OPEN_DRAIN	BIT(3)
+#define GPIOD_FLAGS_BIT_NONEXCLUSIVE	BIT(4)
 
 /**
  * Optional flags that can be passed to one of gpiod_* to configure direction