Re: [PATCH] arm64: dts: rockchip: Add power button for RK3399 Puma

[Quentin Schulz <quentin.schulz@cherry.de>]

Hi Heiko,

On 9/30/24 10:49 AM, Heiko Stübner wrote:
> Hey Quentin, Daniel,
> 
> Am Donnerstag, 26. September 2024, 14:34:30 CEST schrieb Quentin Schulz:
>> On 9/25/24 9:28 AM, Daniel Semkowicz wrote:
>>> There is a PWRBTN# input pin exposed on a Q7 connector. The pin
>>> is routed to a GPIO0_A1 through a diode. Q7 specification describes
>>> the PWRBTN# pin as a Power Button signal.
>>> Configure the pin as KEY_POWER, so it can function as power button and
>>> trigger device shutdown.
>>> Add the pin definition to RK3399 Puma dts, so it can be reused
>>> by derived platforms, but keep it disabled by default.
>>>
>>> Enable the power button input on Haikou development board.
>>>
>>> Signed-off-by: Daniel Semkowicz <dse@thaumatec.com>
>>
>> This works, thanks.
>>
>> Tested-by: Quentin Schulz <quentin.schulz@cherry.de>
>>
>> Now I have some questions I wasn't able to answer myself, maybe someone
>> can provide some feedback on those :)
>>
>> We already have a gpio-keys for buttons on Haikou, c.f.
>> https://elixir.bootlin.com/linux/v6.11/source/arch/arm64/boot/dts/rockchip/rk3399-puma-haikou.dts#L22.
>> Those signals are directly routed to the SoM and follow the Qseven standard.
>>
>> The same applies to PWRBTN# signal.
>>
>> However, here we have one gpio-keys for PWRBTN# in Puma DTSI and one
>> gpio-keys for the buttons and sliders on Haikou devkit in Haikou DTS.
>>
>> I'm a bit undecided on where this should go.
>>
>> Having all button/slider signals following the Qseven standard in Puma
>> DTSI and enable the gpio-keys only in the devkit would make sense to me,
>> so that other baseboards could easily make use of it. However, things
>> get complicated if the baseboard manufacturer decides to only implement
>> **some** of the signals, for which we then need to remove some nodes
>> from gpio-keys (and pinctrl entries) since gpio-keys doesn't check the
>> "status" property in its child nodes (though that could be fixed). At
>> which point, it's not entirely clear if having it in Puma DTSI is
>> actually beneficial.
>>
>> Someone has an opinion/recommendation on that?
> 
> I guess from a platform perspective nobody really cares, so as that is
> "your" board, it comes down to a policy decision on your part ;-) .
> 
> While pins follow the q7 standard, there may very well be some lax
> handling of that standard in some places, and I guess gpio lines could
> be re-used for something else if needed, as something like the lid-switch
> is probably non-essential.
> 
> Also a gpio-key input does not create that much code-overhead if
> replicated, so personally I'd just stick the power-button with the other
> buttons in the haikou dts.
> 
> Which is also a way better thing than having multiple gpio-keys instances
> that userspace then has to handle.
> 

Yes, but this also means "code" duplication for whoever needs this for 
their baseboard, instead of just having to add a &gpio_keys { status = 
"okay"; }.

I don't think there's a good solution here, so I would suggest we go 
with everything in Haikou's gpio-keys as Heiko suggested then, @Daniel 
if you agree can you send a v2 for that?

Thanks!
Quentin

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