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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Date:   Tue, 17 Nov 2020 12:01:59 +0000
From:   Dan Scally <djrscally@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        prabhakar.mahadev-lad.rj@...renesas.com,
        "Krogerus, Heikki" <heikki.krogerus@...ux.intel.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        laurent.pinchart+renesas@...asonboard.com,
        kieran.bingham+renesas@...asonboard.com,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Rob Herring <robh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tian Shu Qiu <tian.shu.qiu@...el.com>,
        Bingbu Cao <bingbu.cao@...el.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Yong Zhi <yong.zhi@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tsuchiya Yuto <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

On 16/11/2020 16:16, Andy Shevchenko wrote:
> On Mon, Nov 16, 2020 at 02:15:01PM +0000, Dan Scally wrote:
>> On 16/11/2020 14:10, Laurent Pinchart wrote:
>>> I thought we were looking for ACPI devices, not companion devices, in
>>> order to extract information from the DSDT and store it in a software
>>> node. I could very well be wrong though.
>> This is correct - the code to fetch the various resources we're looking
>> at all uses acpi_device. Whether using Andy's iterator suggestions or
>> previous bus_for_each_dev(&acpi_bus_type...) I'm just getting the
>> acpi_device via to_acpi_dev() and using that.
> If you try to get an I²C ore SPI device out of pure ACPI device (with given
> APCI _HID) you will fail. So, it's not correct. You are retrieving companion
> devices, while they are still in the struct acpi_device.
>
> And don't ask me, why it's so. I wasn't designed that and didn't affect any
> decision made there.

Well, in terms of the actual device we're getting, I don't think we're
fundamentally doing anything different between the methods...unless I'm
really mistaken.


Originally implementation was like:


const char *supported_devices[] = {

        "OVTI2680",

};


static int cio2_bridge_connect_supported_devices(void)

{

        struct acpi_device *adev;

        int i;

        for (i = 0; i < ARRAY_SIZE(supported_devices); i++) {

                adev =
acpi_dev_get_first_match_dev(supported_devices[i], NULL, -1);

...

}


and acpi_dev_get_first_match_dev() likewise just returns adev via
to_acpi_device(dev).


So, maybe we don't need to do the iterating over all devices with
matching _HID at all, in which case it can be dropped, but if we're
doing it then I can't see that it's different to the original
implementation in terms of the struct acpi_device we're working with or
the route taken to get it.


Either way; ACPI maintainers asked to be CC'd on the next patchset
anyway, so they'll see what we're doing and be able to weigh in.