Re: [PATCH 1/3] dt-bindings: input: cros-ec-keyb: Add a new property

From: Philip Chen <philipchen@chromium.org>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Dmitry Torokhov <dtor@chromium.org>,
	Stephen Boyd <swboyd@chromium.org>,
	Douglas Anderson <dianders@chromium.org>,
	Rajat Jain <rajatja@chromium.org>,
	Benson Leung <bleung@chromium.org>,
	Enric Balletbo i Serra <enric.balletbo@collabora.com>,
	Guenter Roeck <groeck@chromium.org>,
	Rob Herring <robh+dt@kernel.org>, Simon Glass <sjg@chromium.org>,
	devicetree@vger.kernel.org, linux-input@vger.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: input: cros-ec-keyb: Add a new property
Date: Sat, 2 Jan 2021 22:11:21 -0800	[thread overview]
Message-ID: <CA+cxXhkdZ2ifyCG=p3Fbxwnzu-8z3Q1jNzaBQ=MMfeJ3vqkfhw@mail.gmail.com> (raw)
In-Reply-To: <CA+cxXhnY_TpnA1iR8XJ87xNeNsi2Ba89+VJEPtB7wJ-=8O=4ag@mail.gmail.com>

Hi Dmitry,

I have one more question below.
Could you take a look?

On Sat, Jan 2, 2021 at 8:53 PM Philip Chen <philipchen@chromium.org> wrote:
>
> Hi Dmitry,
>
> I see.
> I'll update these patch sets shortly based on your suggestion.
> Thanks.
>
> On Sat, Jan 2, 2021 at 1:04 PM Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> >
> > On Sat, Jan 02, 2021 at 11:39:34AM -0800, Philip Chen wrote:
> > > Hi Dmitry,
> > >
> > > Thanks for reviewing my patch over the holiday season.
> > > Please check my CIL.
> > >
> > > On Mon, Dec 28, 2020 at 10:18 PM Dmitry Torokhov
> > > <dmitry.torokhov@gmail.com> wrote:
> > > >
> > > > Hi Philip,
> > > >
> > > > On Mon, Dec 21, 2020 at 05:47:57PM -0800, Philip Chen wrote:
> > > > > This patch adds a new property `google,custom-keyb-top-row` to the
> > > > > device tree for the custom keyboard top row design.
> > > >
> > > > Why don't we use the property we have for the same purpose in atkbd.c?
> > > > I.e. function-row-physmap?
> > > >
> > > Because this property serves a different purpose than function-row-physmap.
> > > `function-row-physmap` basically links the scancode to the physical
> > > position in the top row.
> > > `google,custom-keyb-top-row` aims at specifying the board-specific
> > > keyboard top row design associated with the action codes.
> > >
> > > In x86 path, the board-specific keyboard top row design associated
> > > with the action codes is exposed from coreboot to kernel through
> > > "linux,keymap" acpi table.
> > > When coreboot generates this acpi table, it asks EC to provide this
> > > information, since we add the board-specific top-row-design in EC
> > > codebase.
> > > (E.g. https://chromium.googlesource.com/chromiumos/platform/ec/+/refs/heads/main/board/jinlon/board.c#396)
> > >
> > > In ARM, we don't plan to involve EC in the vivaldi support stack.
> > > So `google,custom-keyb-top-row` DT property is our replacement for the
> > > board-specific top-row-design in x86 EC codebase.
> >
> > I disagree with this decision. We already have "linux,keymap" property
> > that is supposed to hold accurate keymap for the device in question,
> > there should be no need to introduce yet another property to adjust the
> > keymap to reflect the reality. If a device uses "non classic" ChromeOS
> > top row it should not be using the default keymap from
> > arch/arm/boot/dts/cros-ec-keyboard.dtsi but supply its own. You can
> > consider splitting the keymap into generic lower portion and the top row
> > and moving them into an .h file so they can be easily reused.
> >
> > >
> > > > Also, instead of specifying keycodes in this array we should use
> > > > combination of row and column identifying keys, like this:
> > > >
> > > >         function-row-physmap = <
> > > >                 MATRIX_KEY(0x00, 0x02, KEY_F1),
> > > >                 MATRIX_KEY(0x03, 0x02, KEY_F2),
> > > >                 ...
> > > >         >;
> > >
> > > This mapping between row/column to function keycode is fixed for all
> > > Chrome OS devices.
> >
> > *for now* The mapping for the rest of the keyboard has also stayed
> > static, but we still did not hardcode this information in the driver but
> > rather used DT property to pass it into the kernel.
> >
> > > So we don't really need to host this information in DT.
> > > Instead, I plan to hardcode this information in cros_ec_keyb.c.
> > > (Please see the array "top_row_key_pos[]" in my next patch: "[2/3]
> > > Input: cros_ec_keyb - Support custom top-row keys".)
> > >
> > > The only thing that could make the function-row-physmap file different
> > > among boards is the number of top row keys.
Given the reason above, can we just add `num-top-row-keys` property
instead of the whole `function-row-physmap`?
I think this is the only thing cros_ec_keyb needs to know to generate
the board-specific function-row-physmap file for the userspace.

> > > But this information can be derived from the length of
> > > `google,custom-keyb-top-row`.
> > > So we don't need a separate DT property for it.
> >
> > I am sorry, but I must insist. We need to have:
> >
> > - accurate keymap in linux,keymap property
> > - a separate property describing location of top row keys in terms of
> >   rows and columns (whether we reuse MATRIX_KEY or define another macro
> >   I do not really care).
> >
> > Thanks.
> >
> > --
> > Dmitry