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

From: Daniel Scally <djrscally@gmail.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: 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: Sun, 15 Nov 2020 08:45:06 +0000	[thread overview]
Message-ID: <67d30113-6109-9a1d-5ec7-d8daa90a4f34@gmail.com> (raw)
In-Reply-To: <CAHp75VeGJKMeY-reNWgypVzJ6Myz5S2RXJPHqbPH5kzLYX3G4g@mail.gmail.com>

On 13/11/2020 19:45, Andy Shevchenko wrote:
> On Fri, Nov 13, 2020 at 6:22 PM Laurent Pinchart
> <laurent.pinchart@ideasonboard.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.