Date:   Tue, 1 Dec 2020 20:37:58 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        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,
        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

Hi Sakari,

On Tue, Dec 01, 2020 at 05:55:13PM +0200, Sakari Ailus wrote:
> 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:
> > > > On platforms where ACPI is designed for use with Windows, resources
> > > > that are intended to be consumed by sensor devices are sometimes in
> > > > the _CRS of a dummy INT3472 device upon which the sensor depends. This
> > > > driver binds to the dummy acpi device (which does not represent a
> > > 
> > > acpi device -> acpi_device
> > > 
> > > > physical PMIC) and maps them into GPIO lines and regulators for use by
> > > > the sensor device instead.
> > > 
> > > ...
> > > 
> > > > This patch contains the bits of this process that we're least sure about.
> > > > The sensors in scope for this work are called out as dependent (in their
> > > > DSDT entry's _DEP) on a device with _HID INT3472. These come in at least
> > > > 2 kinds; those with an I2cSerialBusV2 entry (which we presume therefore
> > > > are legitimate tps68470 PMICs that need handling by those drivers - work
> > > > on that in the future). And those without an I2C device. For those without
> > > > an I2C device they instead have an array of GPIO pins defined in _CRS. So
> > > > for example, my Lenovo Miix 510's OVTI2680 sensor is dependent on one of
> > > > the _latter_ kind of INT3472 devices, with this _CRS:
> > > > 
> > > > Method (_CRS, 0, NotSerialized)  // _CRS: Current Resource Settings
> > > > {
> > > >     Name (SBUF, ResourceTemplate ()
> > > >     {
> > > >         GpioIo (Exclusive, PullDefault, 0x0000, 0x0000,
> > > > 	    IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0",
> > > > 	    0x00, ResourceConsumer, ,
> > > >             )
> > > >             {   // Pin list
> > > >                 0x0079
> > > >             }
> > > >         GpioIo (Exclusive, PullDefault, 0x0000, 0x0000,
> > > > 	    IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0",
> > > > 	    0x00, ResourceConsumer, ,
> > > >             )
> > > >             {   // Pin list
> > > >                 0x007A
> > > >             }
> > > >         GpioIo (Exclusive, PullDefault, 0x0000, 0x0000,
> > > > 	    IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0",
> > > > 	    0x00, ResourceConsumer, ,
> > > >             )
> > > >             {   // Pin list
> > > >                 0x008F
> > > >             }
> > > >     })
> > > >     Return (SBUF) /* \_SB_.PCI0.PMI1._CRS.SBUF */
> > > > }
> > > > 
> > > > and the same device has a _DSM Method, which returns 32-bit ints where
> > > > the second lowest byte we noticed to match the pin numbers of the GPIO
> > > > lines:
> > > > 
> > > > Method (_DSM, 4, NotSerialized)  // _DSM: Device-Specific Method
> > > > {
> > > >     If ((Arg0 == ToUUID ("79234640-9e10-4fea-a5c1-b5aa8b19756f")))
> > > >     {
> > > >         If ((Arg2 == One))
> > > >         {
> > > >             Return (0x03)
> > > >         }
> > > > 
> > > >         If ((Arg2 == 0x02))
> > > >         {
> > > >             Return (0x01007900)
> > > >         }
> > > > 
> > > >         If ((Arg2 == 0x03))
> > > >         {
> > > >             Return (0x01007A0C)
> > > >         }
> > > > 
> > > >         If ((Arg2 == 0x04))
> > > >         {
> > > >             Return (0x01008F01)
> > > >         }
> > > >     }
> > > > 
> > > >     Return (Zero)
> > > > }
> > > > 
> > > > We know that at least some of those pins have to be toggled active for the
> > > > sensor devices to be available in i2c, so the conclusion we came to was
> > > > that those GPIO entries assigned to the INT3472 device actually represent
> > > > GPIOs and regulators to be consumed by the sensors themselves. Tsuchiya
> > > > noticed that the lowest byte in the return values of the _DSM method
> > > > seemed to represent the type or function of the GPIO line, and we
> > > > confirmed that by testing on each surface device that GPIO lines where the
> > > > low byte in the _DSM entry for that pin was 0x0d controlled the privacy
> > > > LED of the cameras.
> > > > 
> > > > We're guessing as to the exact meaning of the function byte, but I
> > > > conclude they're something like this:
> > > > 
> > > > 0x00 - probably a reset GPIO
> > > > 0x01 - regulator for the sensor
> > > > 0x0c - regulator for the sensor
> > > > 0x0b - regulator again, but for a VCM or EEPROM
> > > > 0x0d - privacy led (only one we're totally confident of since we can see
> > > >        it happen!)
> > > 
> > > It's solely Windows driver design...
> > > Luckily I found some information and can clarify above table:
> > > 
> > > 0x00 Reset
> > > 0x01 Power down
> > > 0x0b Power enable
> > > 0x0c Clock enable
> > > 0x0d LED (active high)
> > 
> > That's very useful information ! Thank you.
> > 
> > > The above text perhaps should go somewhere under Documentation.
> > 
> > Or in the driver source code, but definitely somewhere else than in the
> > commit message.
> > 
> > > > After much internal debate I decided to write this as a standalone
> > > > acpi_driver. Alternative options we considered:
> > > > 
> > > > 1. Squash all this into the cio2-bridge code, which I did originally write
> > > > but decided I didn't like.
> > > > 2. Extend the existing tps68470 mfd driver...they share an ACPI ID so this
> > > > kinda makes sense, but ultimately given there is no actual physical
> > > > tps68470 in the scenario this patch handles I decided I didn't like this
> > > > either.
> > > 
> > > Looking to this I think the best is to create a module that can be consumed by tps68470 and separately.
> > > So, something near to it rather than under ipu3 hood.
> > > 
> > > You may use same ID's in both drivers (in PMIC less case it can be simple
> > > platform and thus they won't conflict), but both of them should provide GPIO
> > > resources for consumption.
> > > 
> > > 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.
> 
> That's what I thought of, too, as one option, but with some more detail.
> This would be indeed the cleanest option.
> 
> I think it'd be nice if the CLDB stuff (apart from checking whether it's
> there) would be in a different module to avoid cluttering up the real
> tps68470 driver.

Given the amount of code, and the fact that the driver should be
compiled as a module, I don't think it will make a huge difference in
the memory footprint.

-- 
Regards,

Laurent Pinchart

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