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 18:42:29 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Dan Scally <djrscally@...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 Tue, Nov 17, 2020 at 2:02 PM Dan Scally <djrscally@...il.com> wrote:
>
> 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.

Implementation wise the two approaches are quite similar for now, indeed.
I would rather go with an iterator approach for a simple reason, EFI
code already has something which may utilize iterators rather than
using their home grown solution.

-- 
With Best Regards,
Andy Shevchenko