linux-kernel - Re: [PATCH/RFC v9 04/19] mfd: max77693: adjust max77693_led_platform

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Message-id: <548700DE.2050208@samsung.com>
Date:	Tue, 09 Dec 2014 15:02:06 +0100
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	linux-leds@...r.kernel.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, kyungmin.park@...sung.com,
	b.zolnierkie@...sung.com, pavel@....cz, cooloney@...il.com,
	rpurdie@...ys.net, sakari.ailus@....fi, s.nawrocki@...sung.com,
	robh+dt@...nel.org, pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	Chanwoo Choi <cw00.choi@...sung.com>
Subject: Re: [PATCH/RFC v9 04/19] mfd: max77693: adjust
 max77693_led_platform_data

On 12/09/2014 02:50 PM, Lee Jones wrote:
> On Tue, 09 Dec 2014, Jacek Anaszewski wrote:
>
>> On 12/09/2014 11:04 AM, Lee Jones wrote:
>>> On Tue, 09 Dec 2014, Jacek Anaszewski wrote:
>>>
>>>> On 12/09/2014 09:50 AM, Lee Jones wrote:
>>>>> On Wed, 03 Dec 2014, Jacek Anaszewski wrote:
>>>>>
>>>>>> Add "label" array for Device Tree strings with the name of a LED device
>>>>>> and make flash_timeout a two element array, for caching the sub-led
>>>>>> related flash timeout. Added is also an array for caching pointers to the
>>>>>> sub-nodes representing sub-leds.
>>>>>>
>>>>>> Signed-off-by: Jacek Anaszewski <j.anaszewski@...sung.com>
>>>>>> Acked-by: Kyungmin Park <kyungmin.park@...sung.com>
>>>>>> Cc: Chanwoo Choi <cw00.choi@...sung.com>
>>>>>> Cc: Lee Jones <lee.jones@...aro.org>
>>>>>> ---
>>>>>>   include/linux/mfd/max77693.h |    4 +++-
>>>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/include/linux/mfd/max77693.h b/include/linux/mfd/max77693.h
>>>>>> index f0b6585..c80ee99 100644
>>>>>> --- a/include/linux/mfd/max77693.h
>>>>>> +++ b/include/linux/mfd/max77693.h
>>>>>> @@ -88,16 +88,18 @@ enum max77693_led_boost_mode {
>>>>>>   };
>>>>>>
>>>>>>   struct max77693_led_platform_data {
>>>>>> +	const char *label[2];
>>>>>>   	u32 fleds[2];
>>>>>>   	u32 iout_torch[2];for_each_available_child_of_node
>>>>>>   	u32 iout_flash[2];
>>>>>>   	u32 trigger[2];
>>>>>>   	u32 trigger_type[2];
>>>>>> +	u32 flash_timeout[2];
>>>>>>   	u32 num_leds;
>>>>>>   	u32 boost_mode;
>>>>>> -	u32 flash_timeout;
>>>>>>   	u32 boost_vout;
>>>>>>   	u32 low_vsys;
>>>>>> +	struct device_node *sub_nodes[2];
>>>>>
>>>>> I haven't seen anyone do this before.  Why can't you use the provided
>>>>> OF functions to traverse through your tree?
>>>>
>>>> I use for_each_available_child_of_node when parsing DT node, but I
>>>> need to cache the pointer to sub-node to be able to use it later
>>>> when it needs to be passed to V4L2 sub-device which is then
>>>> asynchronously matched by the phandle to sub-node.
>>>>
>>>> If it is not well seen to cache it in the platform data then
>>>> I will find different way to accomplish this.
>>>
>>> I haven't seen the end-driver for this, but why can't you use that
>>> device's of_node pointer?
>>
>> Maybe it is indeed a good idea. I could pass the of_node pointer
>> and the sub-led identifier to the V4L2 sub-device and there look
>> for the sub-node containing relevant identifier. The downside
>> would be only that for_each_available_child_of_node would
>> have to be called twice - in the led driver and in the V4L2 sub-device.
>> I think that we can live with it.
>
> Are the LED and V4L2 drivers children of this MFD?  If so, you can use
> the of_compatible attribute in struct mfd_cell to populate the each
> child's of_node dynamically i.e. the MFD core will do that for you.
>

V4L2 driver wraps LED driver. This way the LED device can be
controlled with use of two interfaces - LED subsystem sysfs
and V4L2 Flash. This is the aim of the whole patch set.

I've thought it over again and it seems that I will need to cache
somewhere these sub_nodes pointers. They have to be easily accessible
for the V4L2 sub-device as it can be asynchronously registered
or unregistered within V4L2 media device. Sub-devices are matched
basing on the sub-node phandle.

Best Regards,
Jacek Anaszewski
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