Re: [PATCHv3 0/2] Driver for TI tlc59116 16 Channel i2c LED driver

[Tomi Valkeinen <tomi.valkeinen-l0cyMroinI0@public.gmane.org>]

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On 20/01/15 15:26, Andrew Lunn wrote:
>> I'm not familiar with the LED/PWM frameworks, so I want to summarize our
>> use case and how I guess this should be done:
>>
>> We use the TLC59108 to provide backlight to a LCD, but in addition to
>> that, it is used as a GPIO expander (or GPO, as it cannot do input). In
>> your earlier patch versions there were some 'gpio' leftovers. Does your
>> board have such GPIO use also?
> 
> No, only LEDs.
>  
>> So my current thinking is that TLC591xx should be a LED driver (as it
>> sounded to me that PWM is not quite suitable for it). On top of that, we
>> need generic 'led-backlight' and 'led-gpio' drivers, each of which uses
>> the given LED driver to do the hardware manipulation, and they expose a
>> backlight device and gpio device, respectively.
> 
> That sounds sensible. led-backlight seems to be mostly implemented
> already via the led trigger code. Adding a minimal backlight_ops does
> not look too hard. You might also be able to do some cleanup of the
> other led based backlight drivers. 
> 
> led-gpio looks like more work, but i don't see why it should not be
> possible. One thing i do need to check is that if the brightness is
> set to 255 the output is not set to 255/256 on and you have a regular
> glitch. For an LED that does not really matter, but for GPIO it would
> not be good.

Right. TLC591xx has the constant output mode which should be used for
GPIO. Perhaps that mode could be always used when the brightness is
turned to maximum. I haven't read the spec carefully enough to know if
there are some downsides.

 Tomi



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