linux-kernel - Re: [PATCH v2 6/7] platform: x86: Add intel_skl

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Date:   Tue, 19 Jan 2021 19:51:14 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Daniel Scally <djrscally@...il.com>, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-i2c@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        devel@...ica.org, rjw@...ysocki.net, lenb@...nel.org,
        andy@...nel.org, mika.westerberg@...ux.intel.com,
        linus.walleij@...aro.org, bgolaszewski@...libre.com,
        wsa@...nel.org, lee.jones@...aro.org, hdegoede@...hat.com,
        mgross@...ux.intel.com, robert.moore@...el.com,
        erik.kaneda@...el.com, sakari.ailus@...ux.intel.com,
        kieran.bingham@...asonboard.com
Subject: Re: [PATCH v2 6/7] platform: x86: Add intel_skl_int3472 driver

On Tue, Jan 19, 2021 at 06:48:15PM +0200, Laurent Pinchart wrote:
> On Tue, Jan 19, 2021 at 01:08:37PM +0200, Andy Shevchenko wrote:
> > On Tue, Jan 19, 2021 at 10:40:42AM +0000, Daniel Scally wrote:
> > > On 19/01/2021 09:24, Andy Shevchenko wrote:
> > > >>>>> +static struct i2c_driver int3472_tps68470 = {
> > > >>>>> +	.driver = {
> > > >>>>> +		.name = "int3472-tps68470",
> > > >>>>> +		.acpi_match_table = int3472_device_id,
> > > >>>>> +	},
> > > >>>>> +	.probe_new = skl_int3472_tps68470_probe,
> > > >>>>> +};
> > > >>> I'm not sure we want to have like this. If I'm not mistaken the I²C driver can
> > > >>> be separated without ACPI IDs (just having I²C IDs) and you may instantiate it
> > > >>> via i2c_new_client_device() or i2c_acpi_new_device() whichever suits better...
> > > >> Sorry, I'm a bit confused by this. The i2c device is already
> > > >> present...we just want the driver to bind to them, so what role do those
> > > >> functions have there?
> > > > What I meant is something like
> > > >
> > > >  *_i2c.c
> > > > 	real I²C driver for the TPS chip, but solely with I²C ID table, no ACPI
> > > > 	involved (and it sounds like it should be mfd/tps one, in which you
> > > > 	just cut out ACPI IDs and convert to pure I²C one, that what I had
> > > > 	suggested in the first place)
> > > 
> > > Ahh; sorry - i misunderstood what you meant there. I understand now I
> > > think, but there is one complication; the ACPI subsystem already creates
> > > a client for that i2c adapter and address; i2c_new_client_device()
> > > includes a check to see whether that adapter / address combination has
> > > an i2c device already.  So we would have to have the platform driver
> > > with ACPI ID first find the existing i2c_client and unregister it before
> > > registering the new one...the existing clients have a name matching the
> > > ACPI device instance name (e.g i2c-INT3472:00) which we can't use as an
> > > i2c_device_id of course.
> > 
> > See how INT33FE is being handled. Hint: drivers/acpi/scan.c:~1600
> > 
> > static const struct acpi_device_id i2c_multi_instantiate_ids[] = {
> > 	{"BSG1160", },
> > 	{"BSG2150", },
> > 	{"INT33FE", },
> > 	{"INT3515", },
> > 	{}
> > };
> > 
> > So, we quirklist it here and instantiate manually from platform driver (new
> > coming one).
> 
> This is documented as used for devices that have multiple I2cSerialBus
> resources. That's not the case for the INT3472 as far as I can tell. I
> don't think we should abuse this mechanism.

This is quite a similar case to that one. Let's avoid yak shaving, right?

> Don't forget that the TPS68470 I2C driver needs to be ACPI-aware, as it
> has to register an OpRegion for ACPI-based Chrome OS devices. On other
> platforms (including DT platforms), it should only register regulators,
> clocks and GPIOs. Given the differences between those platforms, I don't
> think a TPS68470 driver that would fake being unaware of being probed
> through ACPI would be a good idea. We can always refactor the code later
> when we'll have a non-ACPI based platform using the TPS68470, without
> such a platform there's no way we can test the I2C driver without ACPI
> anyway.

Are you agree that MFD approach should stay? How then we can manage to have an
MFD driver cohabit with our new driver? I proposed a clean solution which will
handle all possible cases via quirk driver. Having two drivers enumerated by
different scenarios is a call for troubles (we have already with one of that
sensors).

And there is no "faking" anything, it's rather gating it depending on the
platform.

-- 
With Best Regards,
Andy Shevchenko