linux-kernel - Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger

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Message-ID: <CACna6rzkcpHN8jyB1dXKEgoN6xkO0qUGAjtGs6zEcJoFMo=M8Q@mail.gmail.com>
Date:   Mon, 29 Aug 2016 10:21:48 +0200
From:   Rafał Miłecki <zajec5@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Jacek Anaszewski <j.anaszewski@...sung.com>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Richard Purdie <rpurdie@...ys.net>,
        Felipe Balbi <balbi@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Peter Chen <hzpeterchen@...il.com>,
        "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>,
        Stephan Linz <linz@...pro.net>,
        Matthias Brugger <mbrugger@...e.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:LED SUBSYSTEM" <linux-leds@...r.kernel.org>
Subject: Re: [PATCH RFC V3.5] leds: trigger: Introduce an USB port trigger

On 29 August 2016 at 10:05, Pavel Machek <pavel@....cz> wrote:
>> >2) Having "ports" subdir with RW files, one per each existing physical port
>> >In this situation we don't need "new_port" or "remove_port". If we
>> >want port to be observable we just do:
>> >echo 1 > 1-1
>> >Implementing this solution needs reading more details from USB subsystem.
>>
>> The situation here is clear IMO - the number of USB ports in the system
>> can change dynamically. I'm not sure if this can be handled easily with
>> sysfs, where we usually expose an interface for known set of settings.
>> struct attribute arrays are usually defined statically at the compile
>> time and filled with the variables, that are created with DEVICE_ATTR
>> macro.
>
> sysfs already exposes current view of all usb devices. Just use it.

We're talking about USB ports not devices, but this is still true. You
can find them in
/sys/bus/usb/devices/*/*-port*

I can't see how we could use them. How could I develop sysfs interface
in /sys/class/leds/*/ to allow userspace assigning USB ports to the
LED trigger?

-- 
Rafał