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: <67d30113-6109-9a1d-5ec7-d8daa90a4f34@gmail.com>
Date:   Sun, 15 Nov 2020 08:45:06 +0000
From:   Daniel Scally <djrscally@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     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 13/11/2020 19:45, Andy Shevchenko wrote:
> On Fri, Nov 13, 2020 at 6:22 PM Laurent Pinchart
> <laurent.pinchart@...asonboard.com> wrote:
>> On Fri, Nov 13, 2020 at 10:02:30AM +0000, Dan Scally wrote:
>>> On 29/10/2020 22:51, Laurent Pinchart wrote:
>>>> On Fri, Oct 30, 2020 at 12:22:15AM +0200, Andy Shevchenko wrote:
>>>>> On Thu, Oct 29, 2020 at 11:29:30PM +0200, Laurent Pinchart wrote:
> ...
>
>>>>> In this case we probably need something like
>>>>>
>>>>> struct acpi_device *
>>>>> acpi_dev_get_next_match_dev(struct acpi_device *adev,
>>>>>                        const char *hid, const char *uid, s64 hrv)
>>>>> {
>>>>>    struct device *start = adev ? &adev->dev : NULL;
>>>>>    ...
>>>>>    dev = bus_find_device(&acpi_bus_type, start, &match, acpi_dev_match_cb);
>>>>>    ...
>>>>> }
>>>>>
>>>>> in drivers/acpi/utils.c and
>>>>>
>>>>> static inline struct acpi_device *
>>>>> acpi_dev_get_first_match_dev(const char *hid, const char *uid, s64 hrv)
>>>>> {
>>>>>    return acpi_dev_get_next_match_dev(NULL, hid, uid, hrv);
>>>>> }
>>>>>
>>>>> in include/linux/acpi.h.
>>>>>
>>>>> Then we may add
>>>>>
>>>>> #define for_each_acpi_dev_match(adev, hid, uid, hrv)                       \
>>>>>    for (adev = acpi_dev_get_first_match_dev(hid, uid, hrv);        \
>>>>>         adev;                                                      \
>>>>>         adev = acpi_dev_get_next_match_dev(adev, hid, uid, hrv))
>>>> What the cio2-bridge code needs is indeed
>>>>
>>>>     for each hid in supported hids:
>>>>             for each acpi device that is compatible with hid:
>>>>                     ...
>>>>
>>>> which could also be expressed as
>>>>
>>>>     for each acpi device:
>>>>             if acpi device hid is in supported hids:
>>>>                     ...
>>>>
>>>> I don't mind either option, I'll happily follow the preference of the
>>>> ACPI maintainers.
>>> Does this need raising elsewhere then? The original idea of just
>>> bus_for_each_dev(&acpi_bus_type...) I have now tested and it works fine,
>>> but it does mean that I need to export acpi_bus_type (currently that
>>> symbol's not available)...that seems much simpler to me but I'm not sure
>>> whether that's something to avoid, and if so whether Andy's approach is
>>> better.
>>>
>>> Thoughts?
>> I like simple options :-) A patch to export acpi_bus_type, with enough
>> context in the commit message (and in the cover latter of the series),
>> should be enough to provide all the information the ACPI maintainers
>> need to decide which option is best. With a bit of luck that patch will
>> be considered the best option and no extra work will be needed.
> The problem with ACPI bus is that it is not as simple as other buses,
> i.e. it may have purely ACPI devices along with *companion* devices,
> which are usually represented by platform bus. On top of that for
> several ACPI devices there can be one physical node and it will be not
> so clear what you are exactly looking for by traversing acpi_bus_type.
> I believe it's hidden on purpose.
Alright - I followed your suggestion to implement the iterator instead
then and left acpi_bus_type hidden, thanks.