Re: [RFC 0/4] platform/x86: i2c-multi-instantiate: Pass ACPI fwnode to instantiated i2c-clients

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Hi,

On 11/5/20 11:38 AM, Andy Shevchenko wrote:
> On Thu, Nov 5, 2020 at 10:00 AM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
>>
>> Hi All,
>>
>> As the subject says this series is mostly about passing the ACPI fwnode to
>> i2c-clients instantiated by the i2c-multi-instantiate code.
>>
>> As discussed here:
>> https://bugzilla.kernel.org/show_bug.cgi?id=198671
>>
>> BOSC0200 ACPI devices may sometimes describe 2 accelerometers in a single
>> ACPI device, while working on this I noticed that BOSC0200 ACPI nodes
>> contain ACCEL_MOUNT_MATRIX info (unlike all the other ACPI ids for bmc150
>> accelerometers). Which is why I wanted to pass the fwnode so that we
>> could use this info in the bmc150-accel driver.
>>
>> The plan was to use i2c-multi-instantiate for this, but doing so will
>> change the modalias and /lib/udev/hwdb.d/60-sensor.hwdb matches on
>> the modalias for various quirks setting ACCEL_MOUNT_MATRIX. So then the
>> plan became to first add support for the mount-matrix provided inside
>> the BOSC0200 ACPI node, making the udev info unnecessary. But for at
>> least 1 model (and probably more) the BOSC0200 ACPI node and hwdb info
>> does not match and since the hwdb info is added by users of the actual
>> devices we can assume it is correct, so it seems that we cannot always
>> trust the ACPI provided info.  This is ok, the hwdb info overrides it
>> (iio-sensor-proxy prefers the udev provided mount-matrix over the
>> one provided by the driver) but this means that we MUST keep the
>> existing hwdb matches working, which means that we cannot use
>> i2c-multi-instantiate for this.
>>
>> Instead I will dust of an old patch for this from Jeremy Cline:
>> https://patchwork.kernel.org/project/linux-iio/patch/010001602cf53153-39ad69f1-1b39-4e6d-a748-9455a16c2fbd-000000@xxxxxxxxxxxxxxxxxxx/
>>
>> Which deals with there being 2 accelerometers inside the bmc150-accel
>> driver.
>>
>> But before coming to the conclusion that i2c-multi-instantiate
>> would not work I had already written this series. Since this might
>> be useful for some other case in the future I'm sending this out
>> as a RFC now, mostly so that it gets added to the archives.
> 
> I think they are in pretty good shape (only the 4th required a bit of
> attention).

FWIW I agree with the changes which you suggest for the 4th patch.

> Please, send as non-RFC and also Cc Heikki (just in case if he has
> comments wrt INT3515).

But do we really want to land these changes, while ATM we do not
really have any need for them ?  Esp. the

"platform/x86: i2c-multi-instantiate: Pass ACPI fwnode to instantiated I2C-clients"

Change is not without a chance of regressions. The acpi_device_is_first_physical_node()
behavior surprised me a bit while working on the BOSC0200 changes. So I'm not
100% sure I have managed to see / think of all implications of this change.

Heikki do you now (or in the near future) need access to the fwnode for
the TypeC controllers handled by the i2c-multi-instantiate code ?

Note that if we do decide to move forward with this set, it should probably
be merged in its entirety by Wolfram as it also makes i2c-core changes
(or Wolfram could just merge the i2c-core change and provide an immutable
branch for me to merge into pdx86/for-next.

And then your (Andy's) cleanup series can be applied on top of this once merged.

Regards,

Hans





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