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Date:   Tue, 1 Dec 2020 14:44:02 +0200
From:   Sakari Ailus <sakari.ailus@iki.fi>
To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     Dan Scally <djrscally@gmail.com>, linux-kernel@vger.kernel.org,
        linux-acpi@vger.kernel.org, linux-gpio@vger.kernel.org,
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        andriy.shevchenko@linux.intel.com, linus.walleij@linaro.org,
        bgolaszewski@baylibre.com, wsa@kernel.org, yong.zhi@intel.com,
        sakari.ailus@linux.intel.com, bingbu.cao@intel.com,
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        heikki.krogerus@linux.intel.com
Subject: Re: [PATCH 18/18] ipu3: Add driver for dummy INT3472 ACPI device
Message-ID: <20201201124402.GU4351@valkosipuli.retiisi.org.uk>
References: <20201130133129.1024662-1-djrscally@gmail.com>
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 <20201130205203.GQ4351@valkosipuli.retiisi.org.uk>
 <3e8494a0-a2c0-59e7-46bb-9635c3c239dd@gmail.com>
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 <2a548835-78c6-8fe3-cceb-1fc000707157@gmail.com>
 <20201201123244.GT4351@valkosipuli.retiisi.org.uk>
 <20201201124032.GD4569@pendragon.ideasonboard.com>
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On Tue, Dec 01, 2020 at 02:40:32PM +0200, Laurent Pinchart wrote:
> Hi Sakari,
> 
> On Tue, Dec 01, 2020 at 02:32:44PM +0200, Sakari Ailus wrote:
> > On Tue, Dec 01, 2020 at 08:08:26AM +0000, Dan Scally wrote:
> > > On 01/12/2020 06:44, Sakari Ailus wrote:
> > > > On Mon, Nov 30, 2020 at 11:06:03PM +0000, Dan Scally wrote:
> > > >> On 30/11/2020 20:52, Sakari Ailus wrote:
> > > >>>> +static const struct acpi_device_id int3472_device_id[] = {
> > > >>>> +	{ "INT3472", 0 },
> > > >>>
> > > >>> The INT3472 _HID is really allocated for the tps68470 PMIC chip. It may not
> > > >>> be used by other drivers; people will want to build kernels where both of
> > > >>> these ACPI table layouts are functional.
> > > >>>
> > > >>> Instead, I propose, that you add this as an option to the tps68470 driver
> > > >>> that figures out whether the ACPI device for the tps68470 device actually
> > > >>> describes something else, in a similar fashion you do with the cio2-bridge
> > > >>> driver. I think it may need a separate Kconfig option albeit this and
> > > >>> cio2-bridge cannot be used separately.
> > > >>
> > > >> It actually occurs to me that that may not work (I know I called that
> > > >> out as an option we considered, but that was a while ago actually). The
> > > >> reason I wasn't worried about the existing tps68470 driver binding to
> > > >> these devices is that it's an i2c driver, and these dummy devices don't
> > > >> have an I2cSerialBusV2, so no I2C device is created by them the kernel.
> > > >>
> > > >> Won't that mean the tps68470 driver won't ever be probed for these devices?
> > > >
> > > > Oops. I missed this indeed was not an I?C driver. So please ignore the
> > > > comment.
> > > >
> > > > So I guess this wouldn't be an actual problem. I'd still like to test this
> > > > on a system with tps68470, as the rest of the set.
> > >
> > > On my Go2, it .probes() for the actual tps68740 (that machine has both
> > > types of INT3472 device) but fails with EINVAL when it can't find the
> > > CLDB buffer that these discrete type devices have. My understanding is
> > > that means it's free for the actual tps68470 driver to grab the device;
> > > although that's not happening because I had to blacklist that driver or
> > > it stops the machine from booting at the moment - haven't gotten round
> > > to investigating yet.
> > 
> > Oh, then the problem is actually there. If it probes the tps68470 driver on
> > the systems with Windows ACPI tables, then it should be that driver which
> > works with the Windows ACPI tables, too.
> > 
> > Checking for random objects such as CLDB in multiple drivers and returning
> > an error based on them being there or not wouldn't be exactly neat.
> > Although I'm not sure thare are options that are obviosly pretty here. I
> > wouldn't two separate drivers checking for e.g. CLDB (tps68470 + this one).
> > 
> > The tps68470 driver is an MFD driver that instantiates a number of platform
> > devices. Alternatively, if you make this one a platform device, you can, in
> > case the CLDB (or whatever object) is present, in the tps68470 driver
> > instantiate a device for this driver instead of the rest.
> > 
> > So I'd think what matters is that both drivers can be selected at the same
> > time but the user does not need to manually select them. Both ways could
> > work I guess?
> 
> Let's make it simpler instead of creating lots of devices. Here's what
> I've proposed in a different e-mail in this thread.
> 
> > Given that INT3472 means Intel camera power management device (that's
> > more or less the wording in Windows, I can double-check), would the
> > following make sense ?
> > 
> > A top-level module named intel-camera-pmic (or int3472, or ...) would
> > register two drivers, a platform driver and an I2C driver, to
> > accommodate for both cases ("discrete PMIC" that doesn't have an
> > I2cSerialBusV2, and TPS64870 or uP6641Q that are I2C devices). The probe
> > function would perform the following:
> > 
> > - If there's no CLDB, then the device uses the Chrome OS "ACPI
> >   bindings", and refers to a TPS64870. The code that exists in the
> >   kernel today (registering GPIOs, and registering an OpRegion to
> >   communicate with the power management code in the DSDT) would be
> >   activated.
> > 
> > - If there's a CLDB, then the device type would be retrieved from it:
> > 
> >   - If the device is a "discrete PMIC", the driver would register clocks
> >     and regulators controlled by GPIOs, and create clock, regulator and
> >     GPIO lookup entries for the sensor device that references the PMIC.
> > 
> >   - If the device is a TPS64870, the code that exists in the kernel
> >     today to register GPIOs would be activated, and new code would need
> >     to be written to register regulators and clocks.
> > 
> >   - If the device is a uP6641Q, a new driver will need to be written (I
> >     don't know on which devices this PMIC is used, so this can probably
> >     be deferred).
> > 
> > We can split this in multiple files and/or modules.
> 
> Could you reply to 20201130233232.GD25713@pendragon.ideasonboard.com to
> avoid splitting the conversation ?

Yeah... I hadn't gotten that far yet. :-)

-- 
Sakari Ailus