[v7,06/15] gpio: find gpio base by ascend order

Commit Message

Haojian Zhuang Jan. 18, 2013, 7:31 a.m. UTC

gpiochip_find_base() always tries to find valid gpio with descend order.
It's inconvient if gpio information is passing from DTS. Now try to find
valid gpio with ascend order.

Signed-off-by: Haojian Zhuang <[e-mail]>
---
 drivers/gpio/gpiolib.c |   19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

Comments

Linus Walleij Jan. 21, 2013, 2:24 p.m. UTC | #1

On Fri, Jan 18, 2013 at 8:31 AM, Haojian Zhuang
<[e-mail]> wrote:

> gpiochip_find_base() always tries to find valid gpio with descend order.
> It's inconvient if gpio information is passing from DTS. Now try to find
> valid gpio with ascend order.
>
> Signed-off-by: Haojian Zhuang <[e-mail]>

Grant, can you comment on this?

You know DT and GPIO better than me....

Yours,
Linus Walleij

Grant Likely Feb. 9, 2013, 1:45 p.m. UTC | #2

On Fri, 18 Jan 2013 15:31:10 +0800, Haojian Zhuang <[e-mail]> wrote:
> gpiochip_find_base() always tries to find valid gpio with descend order.
> It's inconvient if gpio information is passing from DTS. Now try to find
> valid gpio with ascend order.

Why is it more convenient? Just to make the numbers smaller? The reason
it uses a descending search is to mimimize the possibility of collision
with fixed GPIO numbers.

g.

Haojian Zhuang Feb. 9, 2013, 5:15 p.m. UTC | #3

On 9 February 2013 21:45, Grant Likely <[e-mail]> wrote:
> On Fri, 18 Jan 2013 15:31:10 +0800, Haojian Zhuang <[e-mail]> wrote:
>> gpiochip_find_base() always tries to find valid gpio with descend order.
>> It's inconvient if gpio information is passing from DTS. Now try to find
>> valid gpio with ascend order.
>
> Why is it more convenient? Just to make the numbers smaller? The reason
> it uses a descending search is to mimimize the possibility of collision
> with fixed GPIO numbers.
>
> g.
>

I tried to parse global gpio number dynamically from DT, so I also used
gpiochip_find_base() to seek gpio number. If it's descending order, all the
gpio number are not also descending order. It will be inconvenient for
linking it to SoC datasheet & schematic. Since changing it to ascending
order may break user space application, Linus NACKed.

Now I'm trying to use fixed gpio number from machine driver.

Regards
Haojian

Patch

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 199fca1..8af57e7 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -128,20 +128,21 @@  static int gpiochip_find_base(int ngpio)
 	int spare = 0;
 	int base = -ENOSPC;
 
-	for (i = ARCH_NR_GPIOS - 1; i >= 0 ; i--) {
+	for (i = 0, base = 0; i < ARCH_NR_GPIOS; i++) {
 		struct gpio_desc *desc = &gpio_desc[i];
 		struct gpio_chip *chip = desc->chip;
 
-		if (!chip && !test_bit(FLAG_RESERVED, &desc->flags)) {
+		if (chip) {
+			spare = 0;
+			i += chip->ngpio - 1;
+			base = i + 1;
+		} else if (test_bit(FLAG_RESERVED, &desc->flags)) {
+			spare = 0;
+			base = i + 1;
+		} else {
 			spare++;
-			if (spare == ngpio) {
-				base = i;
+			if (spare == ngpio)
 				break;
-			}
-		} else {
-			spare = 0;
-			if (chip)
-				i -= chip->ngpio - 1;
 		}
 	}