linux-kernel - Re: [PATCH 1/3] Input: add `SW_BOOT

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Message-ID: <953e4d00-110e-b337-3c6c-af008c843046@theobroma-systems.com>
Date:   Mon, 26 Sep 2022 11:37:45 +0200
From:   Quentin Schulz <quentin.schulz@...obroma-systems.com>
To:     Jeff LaBundy <jeff@...undy.com>
Cc:     Quentin Schulz <foss+kernel@...il.net>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, heiko@...ech.de,
        dmitry.torokhov@...il.com, klaus.goger@...obroma-systems.com,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-input@...r.kernel.org
Subject: Re: [PATCH 1/3] Input: add `SW_BOOT_ALT`

Hi all,

On 9/23/22 19:19, Jeff LaBundy wrote:
[...]
>>
>> I have this switch on the board and I want to expose its state to the user,
>> if this new event code is not possible/a good idea what would you suggest we
>> could use?
>>
>> Note that we already support the same switch but in a different way: https://urldefense.proofpoint.com/v2/url?u=https-3A__git.kernel.org_pub_scm_linux_kernel_git_torvalds_linux.git_tree_arch_arm64_boot_dts_rockchip_rk3399-2Dpuma-2Dhaikou.dts-23n167&d=DwIBAg&c=_sEr5x9kUWhuk4_nFwjJtA&r=LYjLexDn7rXIzVmkNPvw5ymA1XTSqHGq8yBP6m6qZZ4njZguQhZhkI_-172IIy1t&m=vObtDja6hUlL_kVvKRILCvaQfklw1gl7TAW7cm5_9H_Yi00zkzGV6-D3yzazR2gU&s=0Xo-7CDmMoriaTNn_hJdMwftLlcY-tgopPcgzXfQtJE&e=
>> We are just configuring the GPIOs into the GPIO mode with a pull-up, and
>> then it's up to the user to use gpiod or gpio-sysfs to check the state of
>> the GPIO used for this switch. I don't like this, very not user-friendly and
>> was looking for something better :)
> 
> Actually, that's exactly what I was going to suggest. What in particular
> is not user-friendly about it?
> 

The implementation we currently have in place for Puma Haikou is just 
muxing the pins in their GPIO function with a pull-up. Nothing else. 
This means the user still needs to know exactly which GPIO number is for 
which signal/event. Not that great. Also does not allow for a consistent 
user "experience" across modules on the same devkit (different GPIOs 
depending on the SoM).

I had hoped gpio-hog in input mode would expose it to userspace but it 
does not seem to?

Anything to recommend so that we can export a GPIO line for a specific 
function to usersapce without needing the user to know which GPIO number 
they should look at?

While I have your attention, I was wondering about the BATTERY event. We 
have a BATLOW button, following the Q7 standard:
"""
Battery low input. This signal may be driven active low by external
circuitry to signal that the system battery is low or may be used to
signal some other external battery management event.
"""

Oddly vague, but the EV_BATTERY event is not really more precise though 
(at least didn't find more precise information and the introducing 
commit is a bit vague too on the usage). Was just wondering if there was 
any specific usage for this event or if I'm using it correctly here?

Cheers,
Quentin