Re: [PATCH] watchdog_dev: Use device tree alias for naming watchdogs

From: Guenter Roeck
Date: Sat Aug 29 2015 - 05:53:43 EST

On 08/28/2015 02:58 PM, Justin Chen wrote:
Currently there is no way to easily differentiate multiple
watchdog devices. The watchdogs are named by the order they
are probed.
1st probed watchdog: /dev/watchdog0
2nd probed watchdog: /dev/watchdog1

This change uses the alias of the watchdog device node for
the name of the watchdog.
aliases {
watchdog0 = "/...../...."
watchdog3 = "/..../....."
watchdog2 = "/..../....."

This will translate to...

Signed-off-by: Justin Chen <justinpopo6@xxxxxxxxx>

Interesting idea. Checking through other subsystems, many others do the same,
so it makes sense to use that mechanism.

However, the id assignment should be in the calling code, in __watchdog_register_device,
to avoid that another id, possibly conflicting, is assigned through the ida mechanism.

This is a bit more complicated than it looks like to ensure correct id assignment.
Have a look into the i2c code to see how it is handled. Essentially we must pass
the requested number to ida_simple_get().


drivers/watchdog/watchdog_dev.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 6aaefba..52b1f0b 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -41,6 +41,7 @@
#include <linux/miscdevice.h> /* For handling misc devices */
#include <linux/init.h> /* For __init/__exit/... */
#include <linux/uaccess.h> /* For copy_to_user/put_user/... */
+#include <linux/of.h>

#include "watchdog_core.h"

@@ -522,7 +523,13 @@ static struct miscdevice watchdog_miscdev = {

int watchdog_dev_register(struct watchdog_device *watchdog)
- int err, devno;
+ int err, devno, ret;
+ if (watchdog->parent) {
+ ret = of_alias_get_id(watchdog->parent->of_node, "watchdog");
+ if (ret >= 0)
+ watchdog->id = ret;
+ }

if (watchdog->id == 0) {
old_wdd = watchdog;

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