linux-kernel - Re: [PATCH v3 1/2] ACPI / button: Add KEY_LID

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Date:	Mon, 18 Jul 2016 17:51:33 +0200
From:	Bastien Nocera <hadess@...ess.net>
To:	Benjamin Tissoires <benjamin.tissoires@...il.com>,
	Lv Zheng <lv.zheng@...el.com>
Cc:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input <linux-input@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] ACPI / button: Add KEY_LID_CLOSE for new usage
 model

On Mon, 2016-07-18 at 09:53 +0200, Benjamin Tissoires wrote:
> 
<snip>
> I don't think this is a good solution to have a kernel parameter. I
> thought the final decision were to have userspace decide which event
> was valid, and so we just need to export and emit both of events.
> 
> _If_ you export a kernel parameter, it makes sense to have a dmi
> blacklist to have a good default experience, which is what you wanted
> to avoid.
> So if you just export and use both events at the same time, you will
> have:
> - correct ACPI machines will just have an extra KEY_LID_CLOSE event
> emitted, which will not harm logind
> - wrong ACPI machines will not have their SW_LID input event updated
> because it will be kept closed. But given that logind will ignore it,
> there is no harm either
> 
> As Dmitry said, we could also have a KEY_LID_OPEN emitted for
> symmetrical purposes, but I am not entirely sure if this will confuse
> userspace or not. On the other hand, there are few users of these
> states, and we can teach them how to properly use them.
> 
> So in the end, I think you should just get rid of the kernel
> parameter, export SW_LID, KEY_LID_CLOSE, KEY_LID_OPEN in the event
> node, and only add the KEY_LID_CLOSE|OPEN events on an actual acpi
> notification.
> 
> Then a small hwdb entry set will teach logind/powerd if they need to
> ignore the SW_LID event or not.

So user-space would have its own blacklist (likely in udev through an
hwdb), instead of having it in the kernel? That seems like a fine idea
to me, and one of the first consumers, logind, would have all the
necessary data straight away.