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

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Message-ID: <Ze8uxmKoK3baQ5Ah@google.com>
Date: Mon, 11 Mar 2024 09:18:14 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Karel Balej <karelb@...li.ms.mff.cuni.cz>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	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 Mon, Mar 11, 2024 at 11:26:16AM +0100, 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
> 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
> to me to effectively be the same setup as with my driver and that does
> not load automatically (because of the missing alias).

Yes, ioc3kbd is broken as far as module auto-loading goes. It probably
did not get noticed before because the driver is likely to be built-in
on the target architecture.

I'll take patches.

Thanks.

-- 
Dmitry