linux-kernel - Re: [PATCH 2/2] input: Add LED support to Synaptics device

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Message-ID: <s5hy6ghi8d8.wl%tiwai@suse.de>
Date:	Wed, 21 Apr 2010 09:15:47 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Pavel Machek <pavel@....cz>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, Richard Purdie <rpurdie@...ys.net>
Subject: Re: [PATCH 2/2] input: Add LED support to Synaptics device

At Tue, 20 Apr 2010 23:39:54 -0700,
Dmitry Torokhov wrote:
> 
> On Wed, Apr 21, 2010 at 08:31:15AM +0200, Takashi Iwai wrote:
> > At Tue, 20 Apr 2010 22:43:03 -0700,
> > Dmitry Torokhov wrote:
> > > 
> > > On Mon, Apr 19, 2010 at 12:44:08PM +0200, Takashi Iwai wrote:
> > > > At Fri, 16 Apr 2010 10:00:20 +0200,
> > > > I wrote:
> > > > > 
> > > > > At Thu, 15 Apr 2010 21:12:18 +0200,
> > > > > Pavel Machek wrote:
> > > > > > 
> > > > > > Hi!
> > > > > > 
> > > > > > > The new Synaptics devices have an LED on the top-left corner.
> > > > > > > This is controlled via the command 0x0a with parameters 0x88 or 0x10.
> > > > > > > 
> > > > > > > The detection of the LED isn't clear yet.  It should have been the new
> > > > > > > capability bits that indicate the presence, but on real machines, it
> > > > > > > doesn't fit.  So, for the time being, the driver checks the product id
> > > > > > > in the ext capability bits and assumes that LED exists on the known
> > > > > > > devices.
> > > > > > > 
> > > > > > > The support of LED is controlled via a normal input event with EV_LED
> > > > > > > bit mask.  It supports LED_MUTE bit.  X driver can detect the LED
> > > > > > > support by checking these bits.
> > > > > > 
> > > > > > Could we use generic LED API for this?
> > > > > 
> > > > > Yeah, actually I started implementing with LED ADI at first.
> > > > > 
> > > > > But, then it turned out to be that it's much easier to use the
> > > > > existing LED input bits since this LED is really tightly coupled with
> > > > > the synaptics input device.  An individual LED device makes hard to
> > > > > find out the corresponding input device.
> > > > > 
> > > > > If we assume there is only one synaptics and only one synaptics-LED
> > > > > device, then yes, the situation can be a bit easier, though.
> > > > > 
> > > > > > It is not really 'mute' led after all...
> > > > > 
> > > > > If the problem is the misuse of LED_MUTE bit, how about adding a new
> > > > > LED bit, e.g. LED_TOUCHPAD?
> > > > 
> > > > The revised patch with an addition of LED_TOUCHPAD is below.
> > > > 
> > > 
> > > Sorry Takashi, but I will not add any new LED types to input. Even
> > > current input LEDs are going to be accessible thought standard LED
> > > framework (even though I have not apploed Samuel's patch yet I do think
> > > it would move kernel in the right direction).
> > 
> > Hrm, OK, we can live in other way, too.  For touchpad, it wouldn't be
> > a big problem because it's likely a single device.
> > 
> > But, how can we link a led class device and another device, in
> > general?
> 
> I think this question is to Richard, I am a bit fuzzy on LED subsystem.
> But in general I'd expect LED have touchpad input device as parent.

This might work, yes.

> > Also, another remaining question is the lifetime of led device.
> > The mouse device tends to be re-assigned often, e.g. at each time you
> > suspend/hibernate.
> 
> We go to a great lengths to properly resume the device keeping the same
> input_dev structure and the same event node (for historical reasons
> really, nowadays X is hotplug aware so we could do without), do you see
> it being recreated often?

Maybe my test system is old; it's not Xorg 1.8 and not using dynamic X
config.  At least, X driver loses sometimes the device upon resume,
and it required reopening.

> >  Should led device also be removed and revived at
> > each time, or should we keep it and just ignore event?  If we remove
> > it, how can we avoid race?
> 
> I am not sure what race you see - psmouse protocol switch should not
> race so if you remove LED there you shoudl be race-free. If you see
> something racing I am definitely interested in hearing about it.

Well, what I thought of is when the led sysfs doesn't exist even
though the input device is created.  Or, vice versa, the led sysfs
remains while the input device is deactivated.

But this might not be a problem when I create the led device in
probe.  Let's see in the real world.


thanks,

Takashi
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