linux-kernel - Re: [RFC PATCH v3 4/5] input: add onkey driver for Marvell 88PM886 PMIC

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Message-ID: <ce1cac6f-afb9-4388-b709-bfaee0feb525@linaro.org>
Date: Mon, 11 Mar 2024 11:41:53 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Karel Balej <karelb@...li.ms.mff.cuni.cz>,
 Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Lee Jones <lee@...nel.org>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
 Duje Mihanović <duje.mihanovic@...le.hr>,
 ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org
Subject: Re: [RFC PATCH v3 4/5] input: add onkey driver for Marvell 88PM886
 PMIC

On 11/03/2024 11:26, Karel Balej wrote:
> Krzysztof Kozlowski, 2024-03-10T21:35:36+01:00:
>> On 10/03/2024 12:35, Karel Balej wrote:
>>> Dmitry Torokhov, 2024-03-04T17:10:59-08:00:
>>>> On Mon, Mar 04, 2024 at 09:28:45PM +0100, Karel Balej wrote:
>>>>> Dmitry,
>>>>>
>>>>> Dmitry Torokhov, 2024-03-03T12:39:46-08:00:
>>>>>> On Sun, Mar 03, 2024 at 11:04:25AM +0100, Karel Balej wrote:
>>>>>>> From: Karel Balej <balejk@...fyz.cz>
>>>>>>>
>>>>>>> Marvell 88PM886 PMIC provides onkey among other things. Add client
>>>>>>> driver to handle it. The driver currently only provides a basic support
>>>>>>> omitting additional functions found in the vendor version, such as long
>>>>>>> onkey and GPIO integration.
>>>>>>>
>>>>>>> Signed-off-by: Karel Balej <balejk@...fyz.cz>
>>>>>>> ---
>>>>>>>
>>>>>>> Notes:
>>>>>>>     RFC v3:
>>>>>>>     - Drop wakeup-source.
>>>>>>>     RFC v2:
>>>>>>>     - Address Dmitry's feedback:
>>>>>>>       - Sort includes alphabetically.
>>>>>>>       - Drop onkey->irq.
>>>>>>>       - ret -> err in irq_handler and no initialization.
>>>>>>>       - Break long lines and other formatting.
>>>>>>>       - Do not clobber platform_get_irq error.
>>>>>>>       - Do not set device parent manually.
>>>>>>>       - Use input_set_capability.
>>>>>>>       - Use the wakeup-source DT property.
>>>>>>>       - Drop of_match_table.
>>>>>>
>>>>>> I only said that you should not be using of_match_ptr(), but you still
>>>>>> need to have of_match_table set and have MODULE_DEVICE_TABLE() for the
>>>>>> proper module loading support.
>>>>>
>>>>> I removed of_match_table because I no longer need compatible for this --
>>>>> there are no device tree properties and the driver is being instantiated
>>>>> by the MFD driver.
>>>>>
>>>>> Is the MODULE_DEVICE_TABLE() entry needed for the driver to probe when
>>>>> compiled as module? If that is the case, given what I write above, am I
>>>>> correct that MODULE_DEVICE_TABLE(platform,...) would be the right thing
>>>>> to use here?
>>>>
>>>> Yes, if uevent generated for the device is "platform:<name>" then
>>>> MODULE_DEVICE_TABLE(platform,...) will suffice. I am not sure how MFD
>>>> sets it up (OF modalias or platform), but you should be able to check
>>>> the format looking at the "uevent" attribute for your device in sysfs
>>>> (/sys/devices/bus/platform/...). 
>>>
>>> The uevent is indeed platform.
>>>
>>> But since there is only one device, perhaps having a device table is
>>> superfluous and using `MODULE_ALIAS("platform:88pm886-onkey")` is more
>>> fitting?
>>
>> Adding aliases for standard IDs and standard cases is almost never
>> correct. If you need module alias, it means your ID table is wrong (or
>> missing, which is usually wrong).
>>
>>>
>>> Although I don't understand why this is even necessary when the driver
>>> name is such and the module is registered using
>>> `module_platform_driver`...
>>
>> ID table and MODULE_DEVICE_TABLE() are necessary for modprobe to work.
> 
> I think I understand the practical reasons. My point was that I would
> expect the alias to be added automatically even in the case that the
> device table is absent based solely on the driver name and the
> registration method (*module*_*platform*_driver). Why is that not the
> case? Obviously the driver name matching the mfd_cell name is sufficient

You mean add it automatically by macro-magic based on presence of
id_table and/or of_match_table?

That's a good question. I cannot find answer why not, except that maybe
no one ever wrote it...


> for the driver to probe when it is built in so the name does seem to
> serve as some identification for the device just as a device table entry
> would.
> 
> Furthermore, drivers/input/serio/ioc3kbd.c does not seem to have an ID
> table either, nor a MODULE_ALIAS -- is that a mistake? If not, what
> mechanism causes the driver to probe when compiled as a module? It seems

You are now mixing two different things: probing of driver (so bind) and
module auto-loading. Probing is done also by driver name. Auto-loading,
not sure, maybe by name as well? However it is also likely that
auto-loading is broken. Several drivers had such issues in the past.

Best regards,
Krzysztof