Re: [PATCH 0/6] Generic PWM API implementation

[Grant Likely <grant.likely@secretlab.ca>]

On Mon, Nov 23, 2009 at 8:29 AM, Mark Brown
<broonie@opensource.wolfsonmicro.com> wrote:
> On Fri, Nov 20, 2009 at 03:21:31PM -0700, Grant Likely wrote:
>> On Tue, Nov 17, 2009 at 1:27 AM, David Brownell <david-b@pacbell.net> wrote:
>
>> > Since *everything* boils down to one or more signal lines,
>> > your argument leads directly to Linux having no native
>> > hardware interface except GPIOs. ?Not ... practical. ;)
>
>> I think you've missed my point and taken it to an illogical extreme to
>> counter it.  I agree that PWMs are not GPIOs and visa versa.  However,
>> *some* devices are both GPIOs and PWMs.  Also what is needed to manage
>> GPIO and PWM pins is pretty much identical.
>
> On most of the ARM SoCs PWM and GPIO aren't particularly special here -
> most of the on-SoC functionality is multiplexed onto pins through the
> same hardware interface.  A very large proportion of the pins of the SoC
> will have muxes to bring out the signals from the internal IP blocks,
> and pretty much all of those will have GPIO as one of those functions.

Right, pin-mux is a different problem.  But there are also devices
that implement both PWM and GPIO functionality in the same IP block.
I think pin muxing, and pin controller drivers are different problem
domains and should be handled separately.

>> But that *isn't* the primary purpose of the GPIO subsystem.  All that
>> stuff is layered on top of the GPIO pin management code and doesn't
>> really play into this debate.
>
> The GPIO subsystem isn't doing pin management in that way for most
> systems, it's just controlling the GPIO functionality and relies on
> separate configuration to ensure that the relevant pins are in GPIO
> mode.

Sorry. when I said pin management I meant how Linux keeps track of pin
controllers.  Not pin mux.  I should use different terminology perhaps
to reduce confusion.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.