Re: [PATCH 1/2] platform/x86: asus-wmi: Call new led hw_changed API on kbd brightness change

[Bastien Nocera <hadess@hadess.net>]

On Tue, 2018-06-05 at 09:37 +0200, Hans de Goede wrote:
> Hi,
> 
> On 05-06-18 05:18, Chris Chiu wrote:
> > On Tue, Jun 5, 2018 at 10:31 AM, Darren Hart <dvhart@infradead.org>
> > wrote:
> > > 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@redha
> > > > > t.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
> > 
> > That's what I was trying to do in  [PATCH v2] platform/x86: asus-
> > wmi: Add
> > keyboard backlight toggle support. However, that brought another
> > problem
> > discussed in the thread.
> > https://marc.info/?l=linux-kernel&m=152639169210655&w=2
> > 
> > So I moved the brightness change in the driver without passing to
> > userspace.
> > Per Hans, seems there're some other concerns and I also wonder if
> > the
> > TOGGLE event happens in ASUS HID (asus-hid.c) which also convert
> > and
> > pass the keycode to userspace but no TOGGLE key support yet What
> > should
> > we do then?
> 
> As I mentioned in my reply to Darren, there are 2 proper solutions to
> this:
> 
> 1) Make userspace treat KEY_KBDILLUMTOGGLE as a cycle key, this is
> what the kbd-backlight on most laptops with a single hotkey (*) does
> in cases where this is handled in firmware, rather then left to the
> OS. The handled in firmware is the case which I created the
> led_classdev_notify_brightness_hw_changed() API for. This would be
> my preferred solution and I believe that Benjamin is discussing this
> with Bastien ATM.

It isn't on Macs, at least. Toggle is a toggle, not a cycle key. It
turns the keyboard backlight off and on, restoring the backlight level
when turned back on.

> 2) Add a new KEY_KBDILLUMCYCLE event

Which won't be accessible to Xorg.

>  and send that for the TOGGLE code
> on these laptops.
>
> Yes both will take time to get into end-users hand, but so will a
> kernel-only solution. In the mean time endless can always carry
> downstream patches to make things work right now (while waiting for
> the changes to trickle down from upstream).