[Gta04-owner] Linux 3.2-rc2 on GTA04

[Christoph Mair]

On Mon, Nov 21, 2011 at 5:00 PM, Dr. H. Nikolaus Schaller
<hns at goldelico.com> wrote:
>
> Am 21.11.2011 um 16:50 schrieb Christoph Mair:
>
>> On Mon, Nov 21, 2011 at 3:50 PM, Dr. H. Nikolaus Schaller
>> <hns at goldelico.com> wrote:
>>> Am 21.11.2011 um 12:32 schrieb NeilBrown:
>>
>>>> The next big thing I want to work on is proper integration of the LED
>>>> controller - with the 'wlan reset' line looking like a GPIO output rather
>>>> than an LED :-)
>>>
>>> Does this matter?
>> In my opinion: yes.
>>
>>> IMHO it is
>>>
>>>        echo "const1" >somepath and
>>>        echo "const2" >somepath
>>>
>>> So user space daemons should be able to be configured so that it matches
>>> whatever the hardware/kernel needs.
>>>
>>> My idea of the TCA6507 driver was to provide a general I2C LED driver similar
>>> to others. This makes it much more useful to others and raises chance of being
>>> accepted upstream.
>>>
>>> That we mis-use one of the outputs as a WLAN reset, should IMHO not be
>>> hard-coded in the kernel or drivers. It could change for future hardware revisions.
>>> E.g. if we use a WLAN module without reset. Or assign a real GPIO.
>> Nevertheless, if the TCA6507 driver would for example look for a
>> platform_data structure which defines which output is used as GPIO or
>> as LED, it sould be acceptable anyways.
>
> AFAIK, none of the existing LED drivers does this.
> So I would say: don't make it more complicated as it is :)
>
>> In my opinion, the main difference between a LED and a GPIO output is
>> the following: a GPIO does not have a brightness or (probably) should
>> not fade in or out. And this should be handled in software.
>
> Well, there are GPIOs that can also be programmed as PWM outputs.
> So we need some universal output driver that can be configured to behave
> as GPIO, PWM or LED (with different brightness and blinking patterns).
>
> If we want to harmonize that I think it will reach far beyond the GTA04 project...
>
> The main question is: what is a driver? A driver for a specific I2C chip (e.g. TCA6507)
> or for a function (GPIO, PWM, LED).
>
> Or do you just mean that the platform_data should configure each output
> to enable/disable the blinking function? So that nobody can make the WLAN
> reset blink?
I would suggest that the driver registers each output as either LED or
GPIO device, depending on some information (probably available as
platform_data) and maybe using LED as default if nothing is specified.
The TCA6507 would then act as a driver for a multifunction device.
The GPIO part just does not need to handle the blinking as the GPIO
framework does not know about such a function. The LED part should
expose the hardware-blinking feature to the upper layers so that it's
available to the led infrastructure.

> I thought Neil wanted to integrate it into the GPIO framework so that some
> TCA6507 outputs can be controlled as LEDs and others as GPIOs. But I may be
> wrong in my interpretation.
I'm quite sure this is the goal he wants to reach. It probably just
depends on how it's implemented.

Best regards,
  Christoph