Re: [PATCH v4 01/12] DT: leds: Improve description of flash LEDs related properties

[Jacek Anaszewski <j.anaszewski@samsung.com>]

Hi Sakari,

On 04/03/2015 02:09 PM, Sakari Ailus wrote:
> Hi Jacek,
>
> On Tue, Mar 31, 2015 at 03:52:37PM +0200, Jacek Anaszewski wrote:
>> Description of flash LEDs related properties was not precise regarding
>> the state of corresponding settings in case a property is missing.
>> Add relevant statements.
>> Removed is also the requirement making the flash-max-microamp
>> property obligatory for flash LEDs. It was inconsistent as the property
>> is defined as optional. Devices which require the property will have
>> to assert this in their DT bindings.
>>
>> Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
>> Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
>> Cc: Bryan Wu <cooloney@gmail.com>
>> Cc: Richard Purdie <rpurdie@rpsys.net>
>> Cc: Pavel Machek <pavel@ucw.cz>
>> Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
>> Cc: devicetree@vger.kernel.org
>> ---
>>   Documentation/devicetree/bindings/leds/common.txt |   16 +++++++++-------
>>   1 file changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/leds/common.txt b/Documentation/devicetree/bindings/leds/common.txt
>> index 747c538..21a25e4 100644
>> --- a/Documentation/devicetree/bindings/leds/common.txt
>> +++ b/Documentation/devicetree/bindings/leds/common.txt
>> @@ -29,13 +29,15 @@ Optional properties for child nodes:
>>        "ide-disk" - LED indicates disk activity
>>        "timer" - LED flashes at a fixed, configurable rate
>>
>> -- max-microamp : maximum intensity in microamperes of the LED
>> -		 (torch LED for flash devices)
>> -- flash-max-microamp : maximum intensity in microamperes of the
>> -                       flash LED; it is mandatory if the LED should
>> -		       support the flash mode
>> -- flash-timeout-us : timeout in microseconds after which the flash
>> -                     LED is turned off
>> +- max-microamp : Maximum intensity in microamperes of the LED
>> +		 (torch LED for flash devices). If omitted this will default
>> +		 to the maximum current allowed by the device.
>> +- flash-max-microamp : Maximum intensity in microamperes of the flash LED.
>> +		       If omitted this will default to the maximum
>> +		       current allowed by the device.
>> +- flash-timeout-us : Timeout in microseconds after which the flash
>> +                     LED is turned off. If omitted this will default to the
>> +		     maximum timeout allowed by the device.
>>
>>
>>   Examples:
>
> Pavel pointed out that the brightness between maximum current and the
> maximum *allowed* another current might not be noticeable, leading a
> potential spelling error to cause the LED being run at too high current.

I think that a board designed so that it can be damaged because of
software bugs should be considered not eligible for commercial use.
Any self-esteeming manufacturer will not connect a LED to the output
that can produce the current greater than the LED's absolute maximum
current.

The DT properties could be useful for devices like aat1290 device I was
writing a driver for, which has the maximum current and timeout values
depending on corresponding capacitor and resistor values respectively.
Such devices should make the properties required in their bindings.

> The three drivers I've looked also require these properties, which I think
> is in the line with the above.
>
> How about either dropping the patch, or changing maximum to minimum and
> will to should? The drivers could also behave this way instead of requiring
> the properties, but I don't think there's anything wrong with requiring the
> properties either.

As I mentioned in the previous message in this subject, the max-microamp
property refers also to non-flash LEDs. Since existing LED class devices
does not require them, then it should be left optional and default to
max. It would however be inconsistent with flash LEDs related
properties.


> I think this is worth considering now as we can't change this later without
> breaking something.
>

-- 
Best Regards,
Jacek Anaszewski