[PATCH v1 4/8] gpiolib: Get rid of ARCH_NR_GPIOS

[Christophe Leroy]

Since commit 14e85c0e69d5 ("gpio: remove gpio_descs global array")
there is no limitation on the number of GPIOs that can be allocated
in the system since the allocation is fully dynamic.

ARCH_NR_GPIOS is today only used in order to provide downwards
gpiobase allocation from that value, while static allocation is
performed upwards from 0. However that has the disadvantage of
limiting the number of GPIOs that can be registered in the system.

To overcome this limitation without requiring each and every
platform to provide its 'best-guess' maximum number, rework the
allocation to allocate upwards, allowing approx 2 millions of
GPIOs.

In order to still allow static allocation for legacy drivers, define
GPIO_DYNAMIC_BASE with the value 256 as the start for dynamic
allocation.

Signed-off-by: Christophe Leroy <christophe.leroy at csgroup.eu>
---
 arch/arm/include/asm/gpio.h |  1 -
 drivers/gpio/gpio-sta2x11.c |  5 ++--
 drivers/gpio/gpiolib.c      | 10 +++----
 include/asm-generic/gpio.h  | 55 ++++++++++++++-----------------------
 4 files changed, 28 insertions(+), 43 deletions(-)

diff --git a/arch/arm/include/asm/gpio.h b/arch/arm/include/asm/gpio.h
index f3bb8a2bf788..4ebbb58f06ea 100644
--- a/arch/arm/include/asm/gpio.h
+++ b/arch/arm/include/asm/gpio.h
@@ -2,7 +2,6 @@
 #ifndef _ARCH_ARM_GPIO_H
 #define _ARCH_ARM_GPIO_H
 
-/* Note: this may rely upon the value of ARCH_NR_GPIOS set in mach/gpio.h */
 #include <asm-generic/gpio.h>
 
 /* The trivial gpiolib dispatchers */
diff --git a/drivers/gpio/gpio-sta2x11.c b/drivers/gpio/gpio-sta2x11.c
index e07cca0f8d35..1206b2877caa 100644
--- a/drivers/gpio/gpio-sta2x11.c
+++ b/drivers/gpio/gpio-sta2x11.c
@@ -108,8 +108,8 @@ static void gsta_gpio_setup(struct gsta_gpio *chip) /* called from probe */
 	struct gpio_chip *gpio = &chip->gpio;
 
 	/*
-	 * ARCH_NR_GPIOS is currently 256 and dynamic allocation starts
-	 * from the end. However, for compatibility, we need the first
+	 * Dynamic allocation starts at GPIO_DYNAMIC_BASE.
+	 * However, for compatibility, we need the first
 	 * ConneXt device to start from gpio 0: it's the main chipset
 	 * on most boards so documents and drivers assume gpio0..gpio127
 	 */
@@ -129,7 +129,6 @@ static void gsta_gpio_setup(struct gsta_gpio *chip) /* called from probe */
 
 	/*
 	 * After the first device, turn to dynamic gpio numbers.
-	 * For example, with ARCH_NR_GPIOS = 256 we can fit two cards
 	 */
 	if (!gpio_base)
 		gpio_base = -1;
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 3a6f29eeb72d..40ebc3d42a78 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -183,14 +183,14 @@ EXPORT_SYMBOL_GPL(gpiod_to_chip);
 static int gpiochip_find_base(int ngpio)
 {
 	struct gpio_device *gdev;
-	int base = ARCH_NR_GPIOS - ngpio;
+	int base = GPIO_DYNAMIC_BASE;
 
-	list_for_each_entry_reverse(gdev, &gpio_devices, list) {
+	list_for_each_entry(gdev, &gpio_devices, list) {
 		/* found a free space? */
-		if (gdev->base + gdev->ngpio <= base)
+		if (gdev->base >= base + ngpio)
 			break;
-		/* nope, check the space right before the chip */
-		base = gdev->base - ngpio;
+		/* nope, check the space right after the chip */
+		base = gdev->base + gdev->ngpio;
 	}
 
 	if (gpio_is_valid(base)) {
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index aea9aee1f3e9..06a817d9de79 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -11,40 +11,18 @@
 #include <linux/gpio/driver.h>
 #include <linux/gpio/consumer.h>
 
-/* Platforms may implement their GPIO interface with library code,
+/*
+ * Platforms may implement their GPIO interface with library code,
  * at a small performance cost for non-inlined operations and some
  * extra memory (for code and for per-GPIO table entries).
- *
- * While the GPIO programming interface defines valid GPIO numbers
- * to be in the range 0..MAX_INT, this library restricts them to the
- * smaller range 0..ARCH_NR_GPIOS-1.
- *
- * ARCH_NR_GPIOS is somewhat arbitrary; it usually reflects the sum of
- * builtin/SoC GPIOs plus a number of GPIOs on expanders; the latter is
- * actually an estimate of a board-specific value.
  */
 
-#ifndef ARCH_NR_GPIOS
-#if defined(CONFIG_ARCH_NR_GPIO) && CONFIG_ARCH_NR_GPIO > 0
-#define ARCH_NR_GPIOS CONFIG_ARCH_NR_GPIO
-#else
-#define ARCH_NR_GPIOS		512
-#endif
-#endif
-
 /*
- * "valid" GPIO numbers are nonnegative and may be passed to
- * setup routines like gpio_request().  only some valid numbers
- * can successfully be requested and used.
- *
- * Invalid GPIO numbers are useful for indicating no-such-GPIO in
- * platform data and other tables.
+ * At the end we want all GPIOs to be dynamically allocated from 0.
+ * However, some legacy drivers still perform fixed allocation.
+ * Until they are all fixed, leave 0-256 space for them.
  */
-
-static inline bool gpio_is_valid(int number)
-{
-	return number >= 0 && number < ARCH_NR_GPIOS;
-}
+#define GPIO_DYNAMIC_BASE	256
 
 struct device;
 struct gpio;
@@ -140,12 +118,6 @@ static inline void gpio_unexport(unsigned gpio)
 
 #include <linux/kernel.h>
 
-static inline bool gpio_is_valid(int number)
-{
-	/* only non-negative numbers are valid */
-	return number >= 0;
-}
-
 /* platforms that don't directly support access to GPIOs through I2C, SPI,
  * or other blocking infrastructure can use these wrappers.
  */
@@ -169,4 +141,19 @@ static inline void gpio_set_value_cansleep(unsigned gpio, int value)
 
 #endif /* !CONFIG_GPIOLIB */
 
+/*
+ * "valid" GPIO numbers are nonnegative and may be passed to
+ * setup routines like gpio_request().  only some valid numbers
+ * can successfully be requested and used.
+ *
+ * Invalid GPIO numbers are useful for indicating no-such-GPIO in
+ * platform data and other tables.
+ */
+
+static inline bool gpio_is_valid(int number)
+{
+	/* only non-negative numbers are valid */
+	return number >= 0;
+}
+
 #endif /* _ASM_GENERIC_GPIO_H */
-- 
2.37.1