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    SubjectRe: [PATCH 1/3] PWM: add pwm framework support
    On Mon, Jul 04, 2011 at 08:43:23PM +1000, Ryan Mallon wrote:
    > On 04/07/11 17:55, Sascha Hauer wrote:
    > > I am tired of discussing this. It seems we can't agree and unless
    > > someone else jumps in here we will probably have to wait for another
    > > year until something moves in the PWM area.
    > If we are going to introduce a new framework for pwms then we should
    > create one which meets the needs of at least all of the in kernel
    > drivers. This patch series provides no solution for either the atmel or
    > ep93xx drivers, so it is not a complete solution. At some point the
    > api/framework _must_ be changed. If we can introduce transition layers
    > then we should do that now so they we can provide a common framework
    > along with some forward thinking about how the other drivers are going
    > to be migrated to the new framework. This patch series doesn't even
    > migrate _any_ of the existing drivers.
    > It doesn't have to be an all or nothing approach. Possibly Bill's series
    > is perhaps too involved by changing the api, introducing sysfs support
    > and reworking the pwm users. But your series is at the opposite end of
    > the spectrum. It does too little. It will take a few release cycles to
    > get all of the existing drivers migrated and since we can't change the
    > api until that happens the atmel and ep93xx drivers will take longer
    > still. At the very least your series should migrate some of the drivers.
    > The timeline argument is a bit poor. Yes, there has been discussion for
    > a lengthy time about how the pwm api should be developed, but I think
    > that is because it is non-trivial to come up with a framework which is
    > good enough to support all of the pwm hardware (some of which is already
    > in the mainline). Getting something merged now just because it can be
    > done quickly is not a good idea if it all has to get reworked in the
    > future so that it can support all the hardware.
    > The pwm framework needs to incorporate at least the following:
    > - sysfs access (ep93xx driver)

    The sysfs interface will likely raise smoe more discussion, that's why I
    intentionally have no support for it. It can be added later, but right
    now I see no reason why we should add artificial barriers to merge these

    > - Multiple channels per device (atmel driver)

    Again, this can be added later.

    > The mxs driver you introduce looks like it could be implemented as a
    > single device (continuous mmio space) with multiple channels rather than
    > the pwm core/driver approach you have. I also can't see anything in this
    > patch set which hooks up the mxs pwms to an actual board (i.e. nothing
    > calls mxs_add_mxs_pwm)?

    Why should anyone register a device for which no driver is in the tree?

    > The other nice things to have for the pwm framework are:
    > - More fine grained control of pwms: pwm_period_ns, period_duty_ns, etc
    > - Polarity control
    > - Synchronisation support for multi-channel devices
    > - Interrupt handler support
    > - Sleeping vs non-sleeping configuration api
    > The fine-grained control api could be added now. pwm_config could be
    > left as is for the time being (the new api could be a wrapper around it
    > to start with). Polarity control and interrupt handling apis could also
    > be defined without affecting the drivers which don't need to implement
    > them. Multiple channels and the sleeping/non-sleeping api are the more
    > difficult ones, but at least having some sort of indication about how
    > these plan to be solved would be useful.

    Again, why should we add these *now*? It only raises the chance that
    there's more discussion.


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