linux-kernel - Re: [PATCH V5] leds: trigger: Introduce a USB port trigger

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Date:   Fri, 9 Sep 2016 13:05:09 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Peter Chen <hzpeterchen@...il.com>
Cc:     Rafał Miłecki <zajec5@...il.com>,
        Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <j.anaszewski@...sung.com>,
        Felipe Balbi <balbi@...nel.org>, linux-usb@...r.kernel.org,
        Rafał Miłecki <rafal@...ecki.pl>,
        Jonathan Corbet <corbet@....net>,
        Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
        Matthias Brugger <mbrugger@...e.com>,
        Pavel Machek <pavel@....cz>, Stephan Linz <linz@...pro.net>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        "open list:LED SUBSYSTEM" <linux-leds@...r.kernel.org>
Subject: Re: [PATCH V5] leds: trigger: Introduce a USB port trigger

On Fri, Sep 09, 2016 at 05:34:40PM +0800, Peter Chen wrote:
> On Thu, Sep 08, 2016 at 06:08:24PM +0200, Rafał Miłecki wrote:
> > From: Rafał Miłecki <rafal@...ecki.pl>
> > 
> > This commit adds a new trigger responsible for turning on LED when USB
> > device gets connected to the selected USB port. This can can useful for
> > various home routers that have USB port(s) and a proper LED telling user
> > a device is connected.
> > 
> > The trigger gets its documentation file but basically it just requires
> > enabling it and selecting USB ports (e.g. echo 1 > ports/usb1-1).
> > 
> > There was a long discussion on design of this driver. Its current state
> > is a result of picking them most adjustable solution as others couldn't
> > handle all cases.
> > 
> > 1) It wasn't possible for the driver to register separated trigger for
> >    each USB port. Some physical USB ports are handled by more than one
> >    controller and so by more than one USB port. E.g. USB 2.0 physical
> >    port may be handled by OHCI's port and EHCI's port.
> >    It's also not possible to assign more than 1 trigger to a single LED
> >    and implementing such feature would be tricky due to syncing triggers
> >    and sysfs conflicts with old triggers.
> > 
> > 2) Another idea was to register trigger per USB hub. This wouldn't allow
> >    handling devices with multiple USB LEDs and controllers (hubs)
> >    controlling more than 1 physical port. It's common for hubs to have
> >    few ports and each may have its own LED.
> > 
> > This final trigger is highly flexible. It allows selecting any USB ports
> > for any LED. It was also modified (compared to the initial version) to
> > allow choosing ports rather than having user /guess/ proper names. It
> > was successfully tested on SmartRG SR400ac which has 3 USB LEDs,
> > 2 physical ports and 3 controllers.
> > 
> > Another planned feature is support for LED reacting to the USB activity.
> > This can be implemented with another sysfs file for setting mode. The
> > default mode wouldn't change so there won't be ABI breakage and such
> > feature can be safely implemented later.
> > 
> 
> It has such driver at: drivers/usb/common/led.c

Ugh, I thought I had seen something like this before...

Rafał, can you just use this in-kernel code instead?

thanks,

greg k-h