linux-kernel - Re: i2c: introduce i2c helper i2c_find_client_by

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Date:	Sun, 9 Jun 2013 22:53:35 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Bin Gao <bin.gao@...ux.intel.com>
Cc:	Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: i2c: introduce i2c helper i2c_find_client_by_name()

Please, try to avoid top posting in the future emails.

On Fri, Jun 7, 2013 at 12:26 AM, Bin Gao <bin.gao@...ux.intel.com> wrote:
> With v4l2, the camera sensor i2c devices are taken over by v4l2 master
> driver, i.e. ISP driver, and are not expected to be accessed from
> user sapce by ioctl. So ISP driver has to register them by itself to
> get all related information for further communication. Please check
> v4l2_i2c_new_subdev_board() in drivers/media/video/v4l2-common.c for details.

Yes, this is legacy approach for non-DT/non-ACPI5 platforms.

> The platform code can definitely disallow calling i2c_register_board_info()
> to register them but keep the i2c devices list and then let ISP driver register
> them. But, problems come when a single kernel is going to run on two platforms
> - one platform has ACPI5 and the other has SFI.

You have to forget about SFI. Your ISP subdevices use plain platform
data anyway.
In ACPI 5 case v4l2 framework must be extended to cover that case.

> The dynamic unregister and then
> register based on this new helper will not have dependency on firmware interface -
> the same platform code will work for all platforms.

It's not a care of the ISP driver. I think you have to talk to Sakari
about your issues.

> On Thu, Jun 06, 2013 at 11:32:06PM +0300, Andy Shevchenko wrote:
>> On Thu, Jun 6, 2013 at 9:33 PM, Bin Gao <bin.gao@...ux.intel.com> wrote:
>> > There is a requirement to get the i2c_client pointer dynamically without
>> > knowing the bus and slave address. But we do know the client name,
>> > i.e. the name in the i2c_board_info. This patch is to fit this requirement.
>> >
>> > A good example is that an ISP(Imaging Signal Processor) driver needs
>> > register i2c camera sensor devices via v4l2, so it has to unregister
>> > all i2c clients that were previously registered by calling
>> > i2c_register_board_info(), and then re-register. For this case we
>> > can use this helper to get i2c_client by passing the client name.
>>
>> Why ISP driver would like to register sensor drivers in the first place?
>> That seems the task of platform code, or DT, or ACPI5
>>
>> Why do you need to re-register them at run time?

--
With Best Regards,
Andy Shevchenko
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