Re: [PATCH v8 3/3] HID: cp2112: Fwnode Support

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Daniel Kaehn <kaehndan@gmail.com>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>,
	Hans de Goede <hdegoede@redhat.com>,
	robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org,
	jikos@kernel.org, bartosz.golaszewski@linaro.org,
	dmitry.torokhov@gmail.com, devicetree@vger.kernel.org,
	linux-input@vger.kernel.org, ethan.twardy@plexus.com
Subject: Re: [PATCH v8 3/3] HID: cp2112: Fwnode Support
Date: Wed, 8 Mar 2023 14:41:48 +0200	[thread overview]
Message-ID: <ZAiCjBWhEE/dENOJ@smile.fi.intel.com> (raw)
In-Reply-To: <CAP+ZCCe6mdtNmg0QEtQKFCKMyhM9xRffFoMHtxHEGnjNOEAedg@mail.gmail.com>

On Tue, Mar 07, 2023 at 01:57:27PM -0600, Daniel Kaehn wrote:
> On Tue, Mar 7, 2023 at 12:14 PM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> > On Tue, Mar 07, 2023 at 02:17:06PM +0100, Benjamin Tissoires wrote:
> > > On Mar 06 2023, Andy Shevchenko wrote:

...

> > > It is commonly accepted in the ACPI world that the names do not carry
> > > meaning AFAICT, and so I think I agree with Andy's initial comment
> > > regarding using indexes, not names to also fetch the I2C and GPIO nodes.
> > > You can probably have a fallback mechanism for when "i2c" is not
> > > present, or simply check if you are in DT or not and use the names only
> > > if we are in DT.
> >
> > The solution is to provide in the main node the list of cell names, that way
> > you will always know the indices:
> >
> >   Device (DEV) {
> >           _DSD
> >                   "cell-names" { "i2c", "gpio" } // index of the name is the
> >                                                  // index of the cell
> >
> >         Device (I2C0) {
> >         }
> >
> >         Device (GPI0) {
> >         }
> >   }
> >
> > Problem solved.
> 
> Just to make sure I'm understanding you correctly:
> 
> Are you proposing that specifically this driver directly reads "cell-names"
> from the ACPI DSD to implement this indexing? Or are you proposing a
> kernel-wide mechanism of "overriding" a fwnode name with ACPI?
> (assuming this doesn't exist already, and I'm not just missing it in
> the kernel source)
> 
> Or are you proposing something else entirely?
> (apologies if this should be obvious -- throwing up the ACPI newbie
> card again here :) )

Out of the three listed above I'm proposing the first one.
(Maybe it can be called 'reg-names', but it depends on the hardware)

Also look into hierarchical _DSD (it is similar to the children
of the device node without being separate devices).

> In any case, would this be something I should post to the email chain
> with DT and ACPI
> folks for opinions before I start to implement it?

May be, the -names approach is already used widely for clock, interrupt, reset,
phy and nvmem. So it's something we know about.

-- 
With Best Regards,
Andy Shevchenko