Re: [RFC PATCH 00/15] pwm: add support for atomic update

On Wed, 01 Jul 2015 23:57:57 +0200
Heiko Stübner [off-list ref] wrote:

Hi Boris,

Am Mittwoch, 1. Juli 2015, 10:21:46 schrieb Boris Brezillon:

quoted

Hello Thierry,

This series adds support for atomic PWM update, or ITO, the capability
to update all the parameters of a PWM device (enabled/disabled, period,
duty and polarity) in one go.

This implementation is still experimental, and I may have missed some key
aspect, so any feedback are welcome.

Also note that I haven't protected the state update with any locking.
That's because the existing config does not protect against concurrent
access to a requested PWM device (see the pwm_config implementation).
I guess the PWM framework assume the user will implement the proper locking
scheme if it has to concurrently access the device.

The 5 first patches prepare the addition of the pwm_state concept, which
will be used to allow atomic updates.
The following patches introduce the pwm_state struct, initial state
retrieval and atomic update concepts.

Patches 12 and 13 are showing how one can implement the initial state
retrieval and atomic update features in a PWM driver (in this specific
case I implemented it in the rockchip driver).

The last 2 patches are making use of those changes to improve the
pwm-regulator driver (initializing the regulator state based on the
initial PWM state).

at first I got very strange readings (very wrong values and wrong polarity), 
which resulted from the issues I pointed out in the replies to individual 
patches. After fixing these, the pwm read-back now returns exactly the expected 
values :-) .

Sorry about that, as I said I only compile tested the series :-/.
Anyway, thanks for providing fixes for these bugs, they'll be applied
in the next version.

And with the original voltage table from the Chromeos-devicetrees, the pwm-
regulator also returns the expected 1.2V that coreboot initially set.

Great! And thanks for testing the patches.

Best Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com