linux-kernel - Re: [PATCH v3 5/6] platform/x86: Add intel_skl

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Date:   Mon, 22 Feb 2021 13:19:32 +0000
From:   Daniel Scally <djrscally@...il.com>
To:     tfiga@...omium.org, sakari.ailus@...ux.intel.com,
        rajmohan.mani@...el.com, rjw@...ysocki.net, lenb@...nel.org,
        mika.westerberg@...ux.intel.com, linus.walleij@...aro.org,
        bgolaszewski@...libre.com, wsa@...nel.org, lee.jones@...aro.org
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        kieran.bingham+renesas@...asonboard.com,
        laurent.pinchart@...asonboard.com, hdegoede@...hat.com,
        mgross@...ux.intel.com, luzmaximilian@...il.com,
        robert.moore@...el.com, erik.kaneda@...el.com, me@...wu.ch,
        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
Subject: Re: [PATCH v3 5/6] platform/x86: Add intel_skl_int3472 driver

Hi all

On 22/02/2021 13:07, Daniel Scally wrote:
> diff --git a/drivers/platform/x86/intel-int3472/Kconfig b/drivers/platform/x86/intel-int3472/Kconfig
> new file mode 100644
> index 000000000000..b94622245c21
> --- /dev/null
> +++ b/drivers/platform/x86/intel-int3472/Kconfig
> @@ -0,0 +1,31 @@
> +config INTEL_SKL_INT3472
> +	tristate "Intel SkyLake ACPI INT3472 Driver"
> +	depends on ACPI
> +	depends on REGULATOR
> +	depends on GPIOLIB
> +	depends on COMMON_CLK && CLKDEV_LOOKUP
> +	depends on I2C
> +	select MFD_CORE
> +	select REGMAP_I2C
> +	help
> +	  This driver adds support for the INT3472 ACPI devices found on some
> +	  Intel SkyLake devices.
> +
> +	  The INT3472 is an Intel camera power controller, a logical device
> +	  found on some Skylake-based systems that can map to different
> +	  hardware devices depending on the platform. On machines
> +	  designed for Chrome OS, it maps to a TPS68470 camera PMIC. On
> +	  machines designed for Windows, it maps to either a TP68470
> +	  camera PMIC, a uP6641Q sensor PMIC, or a set of discrete GPIOs
> +	  and power gates.
> +
> +	  If your device was designed for Chrome OS, this driver will provide
> +	  an ACPI OpRegion, which must be available before any of the devices
> +	  using it are probed. For this reason, you should select Y if your
> +	  device was designed for ChromeOS. For the same reason the
> +	  I2C_DESIGNWARE_PLATFORM option must be set to Y too.
> +
> +	  Say Y or M here if you have a SkyLake device designed for use
> +	  with Windows or ChromeOS. Say N here if you are not sure.
> +
> +	  The module will be named "intel-skl-int3472"
The Kconfig option for the existing tps68470 driver is a bool which
depends on I2C_DESIGNWARE_PLATFORM=y, giving the following reason:

This option is a bool as it provides an ACPI operation
region, which must be available before any of the devices
using this are probed. This option also configures the
designware-i2c driver to be built-in, for the same reason.

One problem I've faced is that that scenario only applies to some
devices that this new driver can support, so hard-coding it as built in
didn't make much sense. For that reason I opted to set it tristate, but
of course that issue still exists for ChromeOS devices where the
OpRegion will be registered. I opted for simply documenting that
requirement, as is done in aaac4a2eadaa6: "mfd: axp20x-i2c: Document
that this must be builtin on x86", but that's not entirely satisfactory.
Possible alternatives might be setting "depends on
I2C_DESIGNWARE_PLATFORM=y if CHROME_PLATFORMS" or something similar,
though of course the User would still have to realise they need to
build-in the INTEL_SKL_INT3472 Kconfig option too.

Feedback around this issue would be particularly welcome, as I'm not
sure what the best approach might be.