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

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Message-ID: <20160915125629.GH13132@amd>
Date:   Thu, 15 Sep 2016 14:56:29 +0200
From:   Pavel Machek <pavel@....cz>
To:     Rafał Miłecki <zajec5@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Peter Chen <hzpeterchen@...il.com>,
        Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <j.anaszewski@...sung.com>,
        Felipe Balbi <balbi@...nel.org>,
        "linux-usb@...r.kernel.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>,
        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 2016-09-09 13:31:10, Rafał Miłecki wrote:
> On 9 September 2016 at 13:05, Greg KH <gregkh@...uxfoundation.org> wrote:
> > 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?
> 
> I really don't think I can because of all the reasons I carefully
> listed in the commit message.
> 
> Have you took a look at that simple driver? It does nothing I need.
> Its design doesn't allow implementing features I clearly listed in the
> commit message.

In any case, the new driver should probably go near the old one, at
the very least.
									Pavel

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