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

From: Dan Scally <djrscally@gmail.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux Media Mailing List <linux-media@vger.kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	prabhakar.mahadev-lad.rj@bp.renesas.com, "Krogerus,
	Heikki" <heikki.krogerus@linux.intel.com>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	laurent.pinchart+renesas@ideasonboard.com,
	kieran.bingham+renesas@ideasonboard.com,
	Jacopo Mondi <jacopo+renesas@jmondi.org>,
	Rob Herring <robh@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Petr Mladek <pmladek@suse.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Tian Shu Qiu <tian.shu.qiu@intel.com>,
	Bingbu Cao <bingbu.cao@intel.com>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Yong Zhi <yong.zhi@intel.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Tsuchiya Yuto <kitakar@gmail.com>
Subject: Re: [RFC PATCH v3 9/9] ipu3-cio2: Add functionality allowing software_node connections to sensors on platforms designed for Windows
Date: Tue, 17 Nov 2020 12:01:59 +0000	[thread overview]
Message-ID: <3976eac8-2a21-a619-1dba-85212ac4b4b1@gmail.com> (raw)
In-Reply-To: <20201116161636.GC4077@smile.fi.intel.com>

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.