linux-kernel - Re: [PATCH -next 2/2] leds: add /sys/class/leds/<led>/current-trigger

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Date:   Wed, 2 Oct 2019 10:47:03 -0500
From:   Dan Murphy <dmurphy@...com>
To:     Akinobu Mita <akinobu.mita@...il.com>,
        <linux-leds@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>
Subject: Re: [PATCH -next 2/2] leds: add /sys/class/leds/<led>/current-trigger

Akinobu

On 10/2/19 10:13 AM, Akinobu Mita wrote:
> Reading /sys/class/leds/<led>/trigger returns all available LED triggers.
> However, this violates the "one value per file" rule of sysfs.
>
> This provides /sys/class/leds/<led>/current-trigger which is almost
> identical to /sys/class/leds/<led>/trigger.  The only difference is that
> 'current-trigger' only shows the current trigger name.
>
> This new file follows the "one value per file" rule of sysfs.
> We can find all available LED triggers by listing the
> /sys/devices/virtual/led-trigger/ directory.
>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Jacek Anaszewski <jacek.anaszewski@...il.com>
> Cc: Pavel Machek <pavel@....cz>
> Cc: Dan Murphy <dmurphy@...com>
> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> ---
>   Documentation/ABI/testing/sysfs-class-led | 13 +++++++++++
>   drivers/leds/led-class.c                  | 10 ++++++++
>   drivers/leds/led-triggers.c               | 38 +++++++++++++++++++++++++++----
>   drivers/leds/leds.h                       |  5 ++++
>   4 files changed, 62 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
> index 5f67f7a..fdfed3f 100644
> --- a/Documentation/ABI/testing/sysfs-class-led
> +++ b/Documentation/ABI/testing/sysfs-class-led
> @@ -61,3 +61,16 @@ Description:
>   		gpio and backlight triggers. In case of the backlight trigger,
>   		it is useful when driving a LED which is intended to indicate
>   		a device in a standby like state.
> +
> +What:		/sys/class/leds/<led>/current-trigger
> +Date:		September 2019
> +KernelVersion:	5.5
> +Contact:	linux-leds@...r.kernel.org
> +Description:
> +		Set the trigger for this LED. A trigger is a kernel based source
> +		of LED events.
> +		Writing the trigger name to this file will change the current
> +		trigger. Trigger specific parameters can appear in
> +		/sys/class/leds/<led> once a given trigger is selected. For
> +		their documentation see sysfs-class-led-trigger-*.
> +		Reading this file will return the current LED trigger name.

Why do we need this new file can't we just update the current trigger 
file implementation?

I don't see any documentation that states that the read of the trigger 
file will print a list of known triggers.

And writing to the trigger file still works so I would think the _show 
just needs to be fixed.

Besides this patch does not fix the issue in the commit message that the 
trigger file still violates the one value per file rule.

Dan