linux-kernel - Re: [RFC PATCH v3 9/9] ipu3-cio2: Add functionality allowing software_node connections to sensors on platforms designed for Windows

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Message-ID: <98d1f782-9749-1de7-02d5-da51b57ffaef@gmail.com>
Date:   Sat, 24 Oct 2020 23:50:45 +0100
From:   Daniel Scally <djrscally@...il.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linus.walleij@...aro.org, prabhakar.mahadev-lad.rj@...renesas.com,
        heikki.krogerus@...ux.intel.com, dmitry.torokhov@...il.com,
        laurent.pinchart+renesas@...asonboard.com,
        kieran.bingham+renesas@...asonboard.com, jacopo+renesas@...ndi.org,
        robh@...nel.org, davem@...emloft.net, linux@...musvillemoes.dk,
        andriy.shevchenko@...ux.intel.com, sergey.senozhatsky@...il.com,
        rostedt@...dmis.org, pmladek@...e.com, mchehab@...nel.org,
        tian.shu.qiu@...el.com, bingbu.cao@...el.com,
        sakari.ailus@...ux.intel.com, yong.zhi@...el.com,
        rafael@...nel.org, gregkh@...uxfoundation.org, kitakar@...il.com
Subject: Re: [RFC PATCH v3 9/9] ipu3-cio2: Add functionality allowing
 software_node connections to sensors on platforms designed for Windows

Hi Laurent

On 24/10/2020 23:36, Laurent Pinchart wrote:
> Hi Dan,
>
> On Sat, Oct 24, 2020 at 11:28:06PM +0100, Daniel Scally wrote:
>> On 24/10/2020 10:37, Laurent Pinchart wrote:
>>
>>>>> I wonder if we could avoid depending on the I2C device being created by
>>>>> getting the fwnode from adev, and setting ->secondary manually. adev
>>>>> would need to be passed to get_acpi_ssdb_sensor_data() instead of dev.
>>>> Let me try that; I initially wanted to do
>>>> set_secondary_fwnode(&adev->dev, fwnode) to avoid depending on the I2C
>>>> dev being created but it turns out &adev->dev isn't the same pointer. I
>>>> shall try it and see.
>> Actually, thinking on this further I think maybe we can't avoid that -
>> it's not actually in this patch series but during assigning GPIO
>> resources parsed from PMIC's ACPI node to the sensor, I'm using
>> dev_name() on the i2c dev to pass to .dev_id member of gpiod_lookup_table
> Any chance we can construct the I2C device name from the ACPI device,
> the same way that the ACPI/I2C core does ? It may be a dead end, but if
> we could avoid depending on the I2C device, I think it will make
> initialization easier. I have a feeling that will be difficult though,
> as we'll need the I2C bus number, which won't be readily available.

I'd have to look into how the ACPI/I2C core does it to be confident, but
I think it would be ok. Doesn't look to me like the bus number is
involved; my sensor's device names come through as "i2c-OVTI2680:00";
that's just a prefix tacked on to dev_name(adev->dev). I'm sure there's
something that will stop it being quite so easy, but hopefully not
insurmountable.

> Maybe this calls for extending the gpiod lookup API, but that would then
> likely be something we would build on top. I'm thinking about a way to
> specify the GPIO mapping in the software node, and retrieving it from
> there, the same way this is done for GPIOs in OF-based systems.
Yeah that's an option too; I had had the same thought actually. Probably
an extensive piece of work in its own right though