Re: [PATCH] ACPI: dock: Don't eval _STA on every show_docked sysfs read

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 20 Jan 2009 12:18:24 +0100
Holger Macht <hmacht@suse.de> wrote:

> Cc: stable@kernel.org

The patch applied OK to 2.6.28 but not to any earlier kernel.  If we
decide that it should be backported to 2.6.27 or earlier, a new patch
might be needed for that.

> Some devices trigger a DEVICE_CHECK on every evalutation of _STA. This
> can also be seen in commit 8b59560a3baf2e7c24e0fb92ea5d09eca92805db
> (ACPI: dock: avoid check _STA method).  If an undock is processed, the
> dock driver sends a uevent and userspace might read the show_docked
> property in sysfs. This causes an evaluation of _STA of the particular
> device which causes the dock driver to immediately dock again.
> 
> In any case, evaluation of _STA (show_docked) does not necessarily mean
> that we are docked, so check with the internal device structure.
> 
> http://bugzilla.kernel.org/show_bug.cgi?id=12360
> 
> Signed-off-by: Holger Macht <hmacht@suse.de>
> ---
> 
> diff --git a/drivers/acpi/dock.c b/drivers/acpi/dock.c
> index 5b30b8d..afd5db3 100644
> --- a/drivers/acpi/dock.c
> +++ b/drivers/acpi/dock.c
> @@ -855,10 +855,14 @@ fdd_out:
>  static ssize_t show_docked(struct device *dev,
>  			   struct device_attribute *attr, char *buf)
>  {
> +	struct acpi_device *tmp;
> +
>  	struct dock_station *dock_station = *((struct dock_station **)
>  		dev->platform_data);
> -	return snprintf(buf, PAGE_SIZE, "%d\n", dock_present(dock_station));
>  
> +	if (ACPI_SUCCESS(acpi_bus_get_device(dock_station->handle, &tmp)))
> +		return snprintf(buf, PAGE_SIZE, "1\n");
> +	return snprintf(buf, PAGE_SIZE, "0\n");
>  }
>  static DEVICE_ATTR(docked, S_IRUGO, show_docked, NULL);

That seems a little overwrought.  Won't plain old strcpy suffice?


--- a/drivers/acpi/dock.c~acpi-dock-dont-eval-_sta-on-every-show_docked-sysfs-read-simplification
+++ a/drivers/acpi/dock.c
@@ -861,8 +861,8 @@ static ssize_t show_docked(struct device
 		dev->platform_data);
 
 	if (ACPI_SUCCESS(acpi_bus_get_device(dock_station->handle, &tmp)))
-		return snprintf(buf, PAGE_SIZE, "1\n");
-	return snprintf(buf, PAGE_SIZE, "0\n");
+		return strcpy(buf, "1\n");
+	return strcpy(buf, "0\n");
 }
 static DEVICE_ATTR(docked, S_IRUGO, show_docked, NULL);
 
_