linux-kernel - Re: [PATCH 18/18] ipu3: Add driver for dummy INT3472 ACPI device

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Date:   Tue, 1 Dec 2020 20:49:25 +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, linux-media@...r.kernel.org,
        devel@...ica.org, rjw@...ysocki.net, lenb@...nel.org,
        gregkh@...uxfoundation.org, mika.westerberg@...ux.intel.com,
        linus.walleij@...aro.org, bgolaszewski@...libre.com,
        wsa@...nel.org, yong.zhi@...el.com, sakari.ailus@...ux.intel.com,
        bingbu.cao@...el.com, tian.shu.qiu@...el.com, mchehab@...nel.org,
        robert.moore@...el.com, erik.kaneda@...el.com, pmladek@...e.com,
        rostedt@...dmis.org, sergey.senozhatsky@...il.com,
        linux@...musvillemoes.dk, kieran.bingham+renesas@...asonboard.com,
        jacopo+renesas@...ndi.org,
        laurent.pinchart+renesas@...asonboard.com,
        jorhand@...ux.microsoft.com, kitakar@...il.com,
        heikki.krogerus@...ux.intel.com
Subject: Re: [PATCH 18/18] ipu3: Add driver for dummy INT3472 ACPI device

On Tue, Dec 01, 2020 at 01:32:32AM +0200, Laurent Pinchart wrote:
> On Mon, Nov 30, 2020 at 10:07:19PM +0200, Andy Shevchenko wrote:
> > On Mon, Nov 30, 2020 at 01:31:29PM +0000, Daniel Scally wrote:

...

> > So, something like
> > 
> >  tps68470.h with API to consume
> >  split tps68470 to -core, -i2c parts
> >  add int3472, which will serve for above and be standalone platform driver
> >  update cio2-bridge accordingly
> > 
> > Would it be feasible?
> 
> 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.

Seems we can do this, by locating intel_int3472.c under PDx86 hood and dropping
ACPI ID table from TPS68470 MFD driver. The PMIC can be instantiated via
i2c_acpi_new_device() (IIRC the API name).

And actually it makes more sense since it's not and MFD and should not be there.

(Dan, patch wise the one creates intel_int3472.c followed by another one that
 moves ACPI ID from PMIC and introduces its instantiation via I²C board info
 structure)

...

> > > +	table_entry = (struct gpiod_lookup)GPIO_LOOKUP_IDX(acpi_dev_name(adev),
> > > +							   ares->data.gpio.pin_table[0],
> > > +							   func, 0, GPIO_ACTIVE_HIGH);
> > 
> > You won't need this if you have regular INT3472 platform driver.
> > Simple call there _DSM to map resources to the type and use devm_gpiod_get on
> > consumer behalf. Thus, previous patch is not needed.
> 
> How does the consumer (the camera sensor) retrieve the GPIO though ? The
> _DSM is in the PMIC device object, while the real consumer is the camera
> sensor.

1. A GPIO proxy
2. A custom GPIO lookup tables
3. An fwnode passing to the sensor (via swnodes graph)

First may issue deferred probe, while second needs some ordering tricks I guess.
Third one should also provide an ACPI GPIO mapping table or so to make the
consumer rely on names rather than custom numbers.

Perhaps someone may propose other solutions.

-- 
With Best Regards,
Andy Shevchenko