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SubjectRe: [patch/rfc 1/4] GPIO implementation framework
OK, here's the all-in-one patch based on David's most recent gpiolib fix,

Changes include:

1. use per gpio structure "gpio_desc", thus eliminating the restriction of
ARCH_GPIOS_PER_CHIP, thus making it possible leaving no holes in GPIOs
numbering

Note: the number of GPIOs on different GPIO expander chips may vary
much, from 1-2 GPIOs on some audio codecs to dedicated 16-pin GPIO
expander chips. The ARCH_GPIOS_PER_CHIP might not be fair enough.

this change introduces the following small changes:

a) removal of "gpio_chips[]" and use "gpio_desc[]" instead
b) move of "is_out" and "requested" from "struct gpio_chip" to "struct
gpio_desc" and make them bit fields
c) removal of "gpiochip_is_requested()", and use "gpio_desc->requested"
instead

Note: I do want a reference count field within gpio_chip to record the
number of requested GPIOs within the chip, leave this to next patch

d) make gpio_ensure_requested() use gpio_desc, and simplify the code a
bit

2. reduce ARCH_NR_GPIOS to 256, which is moderate for most sane platforms,
and thus saving some memory of the per gpio structures

3. dedicated "gpio_desc.requested_label" field for use with debugfs

4. use a loop for "gpio_desc[]" instead of a loop for "gpio_chips[]" in
gpiolib_show(), change is straight forward; since it is now per gpio
based, the gpio_chip.dbg_show() is removed as well

------ >8 -------

diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index 869b739..e3b2c8f 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -14,14 +14,20 @@
*/

#ifndef ARCH_NR_GPIOS
-#define ARCH_NR_GPIOS 512
-#endif
-
-#ifndef ARCH_GPIOS_PER_CHIP
-#define ARCH_GPIOS_PER_CHIP BITS_PER_LONG
+#define ARCH_NR_GPIOS 256
#endif

struct seq_file;
+struct gpio_chip;
+
+struct gpio_desc {
+ struct gpio_chip *chip;
+ unsigned is_out:1;
+ unsigned requested:1;
+#ifdef CONFIG_DEBUG_FS
+ const char *requested_label;
+#endif
+};

/**
* struct gpio_chip - abstract a GPIO controller
@@ -41,8 +47,6 @@ struct seq_file;
* (base + ngpio - 1).
* @can_sleep: flag must be set iff get()/set() methods sleep, as they
* must while accessing GPIO expander chips over I2C or SPI
- * @is_out: bit array where bit N is true iff GPIO with offset N has been
- * called successfully to configure this as an output
*
* A gpio_chip can help platforms abstract various sources of GPIOs so
* they can all be accessed through a common programing interface.
@@ -65,37 +69,11 @@ struct gpio_chip {
unsigned offset, int value);
void (*set)(struct gpio_chip *chip,
unsigned offset, int value);
- void (*dbg_show)(struct seq_file *s,
- struct gpio_chip *chip);
int base;
u16 ngpio;
unsigned can_sleep:1;
-
- /* other fields are modified by the gpio library only */
- DECLARE_BITMAP(is_out, ARCH_GPIOS_PER_CHIP);
-
-#ifdef CONFIG_DEBUG_FS
- /* fat bits */
- const char *requested[ARCH_GPIOS_PER_CHIP];
-#else
- /* thin bits */
- DECLARE_BITMAP(requested, ARCH_GPIOS_PER_CHIP);
-#endif
};

-/* returns true iff a given gpio signal has been requested;
- * primarily for code dumping gpio_chip state.
- */
-static inline int
-gpiochip_is_requested(struct gpio_chip *chip, unsigned offset)
-{
-#ifdef CONFIG_DEBUG_FS
- return chip->requested[offset] != NULL;
-#else
- return test_bit(offset, chip->requested);
-#endif
-}
-
/* add/remove chips */
extern int gpiochip_add(struct gpio_chip *chip);
extern int __must_check gpiochip_remove(struct gpio_chip *chip);
diff --git a/lib/gpiolib.c b/lib/gpiolib.c
index a853715..f24182e 100644
--- a/lib/gpiolib.c
+++ b/lib/gpiolib.c
@@ -28,39 +28,30 @@
#define extra_checks 0
#endif

-/* gpio_lock protects the table of chips and gpio_chip->requested.
+/* gpio_lock protects the table of gpio_desc[] and desc->requested.
* While any GPIO is requested, its gpio_chip is not removable;
* each GPIO's "requested" flag serves as a lock and refcount.
*/
static DEFINE_SPINLOCK(gpio_lock);
-static struct gpio_chip *chips[DIV_ROUND_UP(ARCH_NR_GPIOS,
- ARCH_GPIOS_PER_CHIP)];
-
+struct gpio_desc gpio_desc[ARCH_NR_GPIOS];

/* Warn when drivers omit gpio_request() calls -- legal but
* ill-advised when setting direction, and otherwise illegal.
*/
-static void gpio_ensure_requested(struct gpio_chip *chip, unsigned offset)
+static void gpio_ensure_requested(struct gpio_desc *desc, unsigned gpio)
{
- int requested;
-
#ifdef CONFIG_DEBUG_FS
- requested = (int) chip->requested[offset];
- if (!requested)
- chip->requested[offset] = "[auto]";
-#else
- requested = test_and_set_bit(offset, chip->requested);
+ if (!desc->requested)
+ desc->requested_label = "(auto)";
#endif
-
- if (!requested)
- printk(KERN_DEBUG "GPIO-%d autorequested\n",
- chip->base + offset);
+ if (!desc->requested)
+ printk(KERN_DEBUG "GPIO-%d autorequested\n", gpio);
}

/* caller holds gpio_lock *OR* gpio is marked as requested */
static inline struct gpio_chip *gpio_to_chip(unsigned gpio)
{
- return chips[gpio / ARCH_GPIOS_PER_CHIP];
+ return gpio_desc[gpio].chip;
}

/**
@@ -75,26 +66,25 @@ static inline struct gpio_chip *gpio_to_chip(unsigned gpio)
int gpiochip_add(struct gpio_chip *chip)
{
unsigned long flags;
- int status = 0;
unsigned id;

- if (chip->base < 0 || (chip->base % ARCH_GPIOS_PER_CHIP) != 0)
- return -EINVAL;
- if ((chip->base + chip->ngpio) >= ARCH_NR_GPIOS)
- return -EINVAL;
- if (chip->ngpio > ARCH_GPIOS_PER_CHIP)
+ if (chip->base < 0 || (chip->base + chip->ngpio) >= ARCH_NR_GPIOS)
return -EINVAL;

spin_lock_irqsave(&gpio_lock, flags);

- id = chip->base / ARCH_GPIOS_PER_CHIP;
- if (chips[id] == NULL)
- chips[id] = chip;
- else
- status = -EBUSY;
+ /* make sure the GPIOs are not claimed by any gpio_chip */
+ for (id = chip->base; id < chip->base + chip->ngpio; id++)
+ if (gpio_desc[id].chip != NULL) {
+ spin_unlock_irqrestore(&gpio_lock, flags);
+ return -EBUSY;
+ }
+
+ for (id = chip->base; id < chip->base + chip->ngpio; id++)
+ gpio_desc[id].chip = chip;

spin_unlock_irqrestore(&gpio_lock, flags);
- return status;
+ return 0;
}
EXPORT_SYMBOL_GPL(gpiochip_add);

@@ -107,28 +97,21 @@ EXPORT_SYMBOL_GPL(gpiochip_add);
int gpiochip_remove(struct gpio_chip *chip)
{
unsigned long flags;
- int status = 0;
- int offset;
- unsigned id = chip->base / ARCH_GPIOS_PER_CHIP;
+ unsigned id;

spin_lock_irqsave(&gpio_lock, flags);

- for (offset = 0; offset < chip->ngpio; offset++) {
- if (gpiochip_is_requested(chip, offset)) {
- status = -EBUSY;
- break;
+ for (id = chip->base; id < chip->base + chip->ngpio; id++)
+ if (gpio_desc[id].requested) {
+ spin_unlock_irqrestore(&gpio_lock, flags);
+ return -EBUSY;
}
- }

- if (status == 0) {
- if (chips[id] == chip)
- chips[id] = NULL;
- else
- status = -EINVAL;
- }
+ for (id = chip->base; id < chip->base + chip->ngpio; id++)
+ gpio_desc[id].chip = NULL;

spin_unlock_irqrestore(&gpio_lock, flags);
- return status;
+ return 0;
}
EXPORT_SYMBOL_GPL(gpiochip_remove);

@@ -139,17 +122,15 @@ EXPORT_SYMBOL_GPL(gpiochip_remove);
*/
int gpio_request(unsigned gpio, const char *label)
{
- struct gpio_chip *chip;
+ struct gpio_desc *desc;
int status = -EINVAL;
unsigned long flags;

spin_lock_irqsave(&gpio_lock, flags);

- chip = gpio_to_chip(gpio);
- if (!chip)
- goto done;
- gpio -= chip->base;
- if (gpio >= chip->ngpio)
+ desc = &gpio_desc[gpio];
+
+ if (desc->chip == NULL)
goto done;

/* NOTE: gpio_request() can be called in early boot,
@@ -157,18 +138,16 @@ int gpio_request(unsigned gpio, const char *label)
*/

status = 0;
-#ifdef CONFIG_DEBUG_FS
- if (!label)
- label = "?";
- if (chip->requested[gpio])
- status = -EBUSY;
+
+ if (!desc->requested)
+ desc->requested = 1;
else
- chip->requested[gpio] = label;
-#else
- if (test_and_set_bit(gpio, chip->requested))
status = -EBUSY;
-#endif

+#ifdef CONFIG_DEBUG_FS
+ if (status == 0)
+ desc->requested_label = (label == NULL) ? "?" : label;
+#endif
done:
spin_unlock_irqrestore(&gpio_lock, flags);
return status;
@@ -178,27 +157,23 @@ EXPORT_SYMBOL_GPL(gpio_request);
void gpio_free(unsigned gpio)
{
unsigned long flags;
- struct gpio_chip *chip;
+ struct gpio_desc *desc;

spin_lock_irqsave(&gpio_lock, flags);

- chip = gpio_to_chip(gpio);
- if (!chip)
- goto done;
- gpio -= chip->base;
- if (gpio >= chip->ngpio)
+ desc = &gpio_desc[gpio];
+
+ if (desc->chip == NULL)
goto done;

-#ifdef CONFIG_DEBUG_FS
- if (chip->requested[gpio])
- chip->requested[gpio] = NULL;
+ if (desc->requested)
+ desc->requested = 0;
else
- chip = NULL;
-#else
- if (!test_and_clear_bit(gpio, chip->requested))
- chip = NULL;
+ WARN_ON(extra_checks);
+
+#ifdef CONFIG_DEBUG_FS
+ desc->requested_label = NULL;
#endif
- WARN_ON(extra_checks && chip == NULL);
done:
spin_unlock_irqrestore(&gpio_lock, flags);
}
@@ -218,17 +193,22 @@ int gpio_direction_input(unsigned gpio)
{
unsigned long flags;
struct gpio_chip *chip;
+ struct gpio_desc *desc;
int status = -EINVAL;

spin_lock_irqsave(&gpio_lock, flags);

- chip = gpio_to_chip(gpio);
+ desc = &gpio_desc[gpio];
+ chip = desc->chip;
+
+ gpio_ensure_requested(desc, gpio);
+
if (!chip || !chip->get || !chip->direction_input)
goto fail;
+
gpio -= chip->base;
if (gpio >= chip->ngpio)
goto fail;
- gpio_ensure_requested(chip, gpio);

/* now we know the gpio is valid and chip won't vanish */

@@ -237,8 +217,8 @@ int gpio_direction_input(unsigned gpio)
might_sleep_if(extra_checks && chip->can_sleep);

status = chip->direction_input(chip, gpio);
- if (status == 0)
- clear_bit(gpio, chip->is_out);
+ if (status)
+ desc->is_out = 0;
return status;
fail:
spin_unlock_irqrestore(&gpio_lock, flags);
@@ -250,17 +230,22 @@ int gpio_direction_output(unsigned gpio, int value)
{
unsigned long flags;
struct gpio_chip *chip;
+ struct gpio_desc *desc;
int status = -EINVAL;

spin_lock_irqsave(&gpio_lock, flags);

- chip = gpio_to_chip(gpio);
+ desc = &gpio_desc[gpio];
+ chip = desc->chip;
+
+ gpio_ensure_requested(desc, gpio);
+
if (!chip || !chip->set || !chip->direction_output)
goto fail;
+
gpio -= chip->base;
if (gpio >= chip->ngpio)
goto fail;
- gpio_ensure_requested(chip, gpio);

/* now we know the gpio is valid and chip won't vanish */

@@ -269,8 +254,8 @@ int gpio_direction_output(unsigned gpio, int value)
might_sleep_if(extra_checks && chip->can_sleep);

status = chip->direction_output(chip, gpio, value);
- if (status == 0)
- set_bit(gpio, chip->is_out);
+ if (status)
+ desc->is_out = 1;
return status;
fail:
spin_unlock_irqrestore(&gpio_lock, flags);
@@ -363,27 +348,29 @@ EXPORT_SYMBOL_GPL(gpio_set_value_cansleep);
#include <linux/debugfs.h>
#include <linux/seq_file.h>

-
-static void gpiolib_dbg_show(struct seq_file *s, struct gpio_chip *chip)
+static int gpiolib_show(struct seq_file *s, void *unused)
{
- unsigned i;
+ struct gpio_chip *chip;
+ unsigned id;

- for (i = 0; i < chip->ngpio; i++) {
- unsigned gpio;
- int is_out;
+ /* REVISIT this isn't locked against gpio_chip removal ... */

- if (!chip->requested[i])
- continue;
+ seq_printf(s, "gpio chip_name requested direction value irq\n");

- gpio = chip->base + i;
- is_out = test_bit(i, chip->is_out);
+ for (id = 0; id < ARCH_NR_GPIO; id++) {
+ struct gpio_desc *desc = &gpio_desc[id];
+ struct gpio_chip *chip = desc->chip;
+
+ if (chip == NULL)
+ continue;

- seq_printf(s, " gpio-%-3d (%-12s) %s %s",
- gpio, chip->requested[i],
- is_out ? "out" : "in ",
- chip->get
- ? (chip->get(chip, i) ? "hi" : "lo")
- : "? ");
+ seq_printf(s, " %3d %12s %9s %9s %5s", gpio,
+ chip->label,
+ desc->requested_label,
+ (desc->is_out) ? "out" : "in",
+ (chip->get) ?
+ (chip->get(chip, i) ? "hi" : "lo")
+ : "?");

if (!is_out) {
int irq = gpio_to_irq(gpio);
@@ -431,32 +418,6 @@ static void gpiolib_dbg_show(struct seq_file *s,
struct gpio_chip *chip)

seq_printf(s, "\n");
}
-}
-
-static int gpiolib_show(struct seq_file *s, void *unused)
-{
- struct gpio_chip *chip;
- unsigned id;
- int started = 0;
-
- /* REVISIT this isn't locked against gpio_chip removal ... */
-
- for (id = 0; id < ARRAY_SIZE(chips); id++) {
- chip = chips[id];
- if (!chip)
- continue;
-
- seq_printf(s, "%sGPIOs %d-%d, %s%s:\n",
- started ? "\n" : "",
- chip->base, chip->base + chip->ngpio - 1,
- chip->label ? : "generic",
- chip->can_sleep ? ", can sleep" : "");
- started = 1;
- if (chip->dbg_show)
- chip->dbg_show(s, chip);
- else
- gpiolib_dbg_show(s, chip);
- }
return 0;
}

------ >8 -------
On Nov 27, 2007 9:46 AM, David Brownell <david-b@pacbell.net> wrote:
> On Tuesday 13 November 2007, David Brownell wrote:
> > So the point of these is to make it easier for platforms
> > (or even just boards) to make sure the GPIO number space
> > is densely packed, rather than loosely so? Paying about
> > 2KBytes for that privilege. (Assuming a 32 bit system
> > with 256 GPIOs.)
> >
> > I could see that being a reasonable tradeoff. I wouldn't
> > have started there myself, but you know how that goes!
> >
> > Does anyone else have any comments on that issue?
>
> Nobody else seems to have any comments on Eric's series
> of patches to add a gpio_desc layer ... whereas, I was
> looking at updating one platform, and got annoyed at some
> stuff that would have been non-issues with them in place!
>
>
> Eric, would you feel like rolling an all-in-one patch against
> the gpiolib support from 2.6.24-rc3-mm? Including updated
> versions of your patches:
>
> - [PATCH 2/5] define gpio_chip.requested_str
> (renaming it as "label" to match its usage)
> - [PATCH 3/5] use a per GPIO "struct gpio_desc"
> (but without that needless list; for debug,
> just scan the gpio_desc list for the next
> non-null chip)
> - [PATCH] move per GPIO "is_out" to "struct gpio_desc"
> (i.e. patch 4/5)
> - [PATCH 5/5] move per GPIO "requested" to "struct gpio_desc"
> (and "label" too)
>
> along with removing the ARCH_GPIOS_PER_CHIP symbol, and
> reducing ARCH_NR_GPIOS to a value which will waste less
> space by default? (Like maybe 256.)
>
> I think an all-in-one patch will be easier to review
> and agree on including (or not).
>
> - Dave
>

--
Cheers
- eric
-
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