linux-kernel - Re: [PATCH 1/2] platform/x86: asus-wmi: Call new led hw

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Message-ID: <20180605023124.GE47042@localhost.localdomain>
Date:   Mon, 4 Jun 2018 19:31:24 -0700
From:   Darren Hart <dvhart@...radead.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Daniel Drake <drake@...lessm.com>, Chris Chiu <chiu@...lessm.com>,
        Corentin Chary <corentin.chary@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        acpi4asus-user <acpi4asus-user@...ts.sourceforge.net>,
        Linux Upstreaming Team <linux@...lessm.com>,
        Bastien Nocera <hadess@...ess.net>,
        Benjamin Berg <benjamin@...solutions.net>
Subject: Re: [PATCH 1/2] platform/x86: asus-wmi: Call new led hw_changed API
 on kbd brightness change

On Mon, Jun 04, 2018 at 04:23:04PM +0200, Hans de Goede wrote:
> Hi,
> 
> On 04-06-18 15:51, Daniel Drake wrote:
> > On Mon, Jun 4, 2018 at 7:22 AM, Hans de Goede <hdegoede@...hat.com> wrote:
> > > Is this really a case of the hardware itself processing the
> > > keypress and then changing the brightness *itself* ?
> > > 
> > >  From the "[PATCH 2/2] platform/x86: asus-wmi: Add keyboard backlight
> > > toggle support" patch I get the impression that the driver is
> > > modifying the brightness from within the kernel rather then the
> > > keyboard controller are ACPI embeddec-controller doing it itself.
> > > 
> > > If that is the case then the right fix is for the driver to stop
> > > mucking with the brighness itself, it should simply report the
> > > right keyboard events and export a led interface and then userspace
> > > will do the right thing (and be able to offer flexible policies
> > > to the user).
> > 
> > Before this modification, the driver reports the brightness keypresses
> > to userspace and then userspace can respond by changing the brightness
> > level, as you describe.
> > 
> > You are right in that the hardware doesn't change the brightness
> > directly itself, which is the normal usage of LED_BRIGHT_HW_CHANGED.
> > 
> > However this approach was suggested by Benjamin Berg and Bastien
> > Nocera in the thread: Re: [PATCH v2] platform/x86: asus-wmi: Add
> > keyboard backlight toggle support
> > https://marc.info/?l=linux-kernel&m=152639169210655&w=2
> > 
> > The issue is that we need to support a new "keyboard backlight
> > brightness cycle" key (in the patch that follows this one) which
> > doesn't fit into any definitions of keys recognised by the kernel and
> > likewise there's no userspace code to handle it.
> > 
> > If preferred we could leave the standard brightness keys behaving as
> > they are (input events) and make the new special key type directly
> > handled by the kernel?
> 
> I'm sorry that Benjamin and Bastien steered you in this direction,
> IMHO none of it should be handled in the kernel.
> 
> Anytime any sort of input is directly responded to by the kernel
> it is a huge PITA to deal with from userspace. The kernel will have
> a simplistic implementation which almost always is wrong.
> 
> Benjamin, remember the pain we went through with rfkill hotkey
> presses being handled in the kernel ?
> 
> And then there is the whole acpi_video.brightness_switch_enabled
> debacle, which is an option which defaults to true which causes
> the kernel to handle LCD brightness key presses, which all distros
> have been patching to default to off for ages.
> 
> To give a concrete example, we may want to implement software
> dimming / auto-off of the kbd backlight when the no keys are
> touched for x seconds. This would seriously get in the way of that.
> 
> So sorry, but NACK to this series.

So if instead of modifying the LED value, the kernel platform drivers
converted the TOGGLE into a cycle even by converting to an UP event
based on awareness of the plaform specific max value and the read
current value, leaving userspace to act on the TOGGLE/UP events - would
that be preferable?

Something like:

	if (code == TOGGLE && ledval < ledmax)
		code = UP;

	sparse_keymap_report_event(..., code, ...)

}
-- 
Darren Hart
VMware Open Source Technology Center