Patchwork [1/3] PWM: add pwm framework support

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Submitter Sascha Hauer
Date Dec. 7, 2011, 9:07 a.m.
Message ID <20111207090734.GN27267@pengutronix.de>
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Permalink /patch/129919/
State New
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Pull-request

git://git.pengutronix.de/git/imx/linux-2.6.git pwmlib

Comments

Sascha Hauer - Dec. 7, 2011, 9:07 a.m.
On Wed, Dec 07, 2011 at 09:53:39AM +0100, Thierry Reding wrote:
> * Arnd Bergmann wrote:
> > On Monday 04 July 2011, Sascha Hauer wrote:
> > > On Mon, Jul 04, 2011 at 08:43:23PM +1000, Ryan Mallon wrote:
> > >
> > > > 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.
> > 
> > My impression is that there are a lot of things that could easily be
> > done to improve the state of PWM drivers, but I don't care about the
> > order in which they are done. My main issue is the lack of a subsystem
> > core driver, which both you and Bill have patches for. It's clear that
> > other people have other issues and want to see their problems addressed
> > first.
> > 
> > I also think that the pwm code is simple enough that we don't have
> > to worry too much about the order that things are done in. Any patch
> > that is making the code better should just get in and not have to
> > wait for something else to be completed first.
> > 
> > What we do need now is a maintainer that can coordinate the patches
> > and merge the ones that have been agreed on. Or multiple maintainers.
> 
> Hi,
> 
> I'm looking at adding DT support for pwm-backlight, and I think a central PWM
> API will be required first. Looking through the archives this seems to be the
> last activity in that direction. Perhaps we can get the efforts restarted?
> 
> I pretty much agree with Arnd and Sascha here in that we should try to get a
> basic framework added. Everything else can be added on top later.

I have a branch which adds a basic PWM framework. It doesn't change the
pwm API at all, but only adds support for registering multiple PWM
drivers. All in Kernel drivers are converted to this new framework, but
except the i.MX driver all of them are untested. I'm quite confident
that the drivers itself work, but there will probably be some Kconfig
related issues which I wasn't able to sort out. The corresponding
Maintainers should probably have a look over it. Feel free to post
the patches if you are prepared to work on the comments you receive.
Otherwise I'll see if I find some time maybe next week.

Sascha


You can find my latest work on this here:


The following changes since commit c3b92c8787367a8bb53d57d9789b558f1295cc96:

  Linux 3.1 (2011-10-24 09:10:05 +0200)

are available in the git repository at:
  git://git.pengutronix.de/git/imx/linux-2.6.git pwmlib

Sascha Hauer (7):
      PWM: add pwm framework support
      ARM mxs: adjust pwm resources to what the driver expects
      pwm: Add a i.MX23/28 pwm driver
      ARM i.MX: Move i.MX pwm driver to pwm framework
      ARM pxa: Move pxa pwm driver to pwm framework
      ARM Samsung: Move s3c pwm driver to pwm framework
      ARM vt8500: Move vt8500 pwm driver to pwm framework

 Documentation/pwm.txt                              |   56 ++++
 MAINTAINERS                                        |    6 +
 arch/arm/mach-mxs/devices/platform-mxs-pwm.c       |   32 ++-
 arch/arm/mach-pxa/Kconfig                          |   14 -
 arch/arm/plat-mxc/Kconfig                          |    6 -
 arch/arm/plat-mxc/Makefile                         |    1 -
 arch/arm/plat-pxa/Makefile                         |    1 -
 arch/arm/plat-samsung/Makefile                     |    4 -
 drivers/Kconfig                                    |    2 +
 drivers/Makefile                                   |    1 +
 drivers/pwm/Kconfig                                |   32 ++
 drivers/pwm/Makefile                               |    6 +
 drivers/pwm/core.c                                 |  220 ++++++++++++++
 arch/arm/plat-mxc/pwm.c => drivers/pwm/imx-pwm.c   |  102 ++-----
 drivers/pwm/mxs-pwm.c                              |  312 ++++++++++++++++++++
 arch/arm/plat-pxa/pwm.c => drivers/pwm/pxa-pwm.c   |  118 +++-----
 .../pwm.c => drivers/pwm/samsung-pwm.c             |  108 ++-----
 .../mach-vt8500/pwm.c => drivers/pwm/vt8500-pwm.c  |  103 ++-----
 include/linux/pwm.h                                |   37 +++
 19 files changed, 832 insertions(+), 329 deletions(-)
 create mode 100644 Documentation/pwm.txt
 create mode 100644 drivers/pwm/Kconfig
 create mode 100644 drivers/pwm/Makefile
 create mode 100644 drivers/pwm/core.c
 rename arch/arm/plat-mxc/pwm.c => drivers/pwm/imx-pwm.c (78%)
 create mode 100644 drivers/pwm/mxs-pwm.c
 rename arch/arm/plat-pxa/pwm.c => drivers/pwm/pxa-pwm.c (72%)
 rename arch/arm/plat-samsung/pwm.c => drivers/pwm/samsung-pwm.c (80%)
 rename arch/arm/mach-vt8500/pwm.c => drivers/pwm/vt8500-pwm.c (75%)
Thierry Reding - Dec. 14, 2011, 10:03 a.m.
* Sascha Hauer wrote:
> I have a branch which adds a basic PWM framework. It doesn't change the
> pwm API at all, but only adds support for registering multiple PWM
> drivers. All in Kernel drivers are converted to this new framework, but
> except the i.MX driver all of them are untested. I'm quite confident
> that the drivers itself work, but there will probably be some Kconfig
> related issues which I wasn't able to sort out. The corresponding
> Maintainers should probably have a look over it. Feel free to post
> the patches if you are prepared to work on the comments you receive.
> Otherwise I'll see if I find some time maybe next week.
[...]

I've looked at this in more detail and one thing that irritates me is that
the current driver API requires a driver to register a pwm_chip structure for
each PWM it can control. Wouldn't it be easier in such cases to just specify
how many PWMs a chip wants to register, much like gpiolib does it?

Thierry
Sascha Hauer - Dec. 14, 2011, 11:37 a.m.
On Wed, Dec 14, 2011 at 11:03:38AM +0100, Thierry Reding wrote:
> * Sascha Hauer wrote:
> > I have a branch which adds a basic PWM framework. It doesn't change the
> > pwm API at all, but only adds support for registering multiple PWM
> > drivers. All in Kernel drivers are converted to this new framework, but
> > except the i.MX driver all of them are untested. I'm quite confident
> > that the drivers itself work, but there will probably be some Kconfig
> > related issues which I wasn't able to sort out. The corresponding
> > Maintainers should probably have a look over it. Feel free to post
> > the patches if you are prepared to work on the comments you receive.
> > Otherwise I'll see if I find some time maybe next week.
> [...]
> 
> I've looked at this in more detail and one thing that irritates me is that
> the current driver API requires a driver to register a pwm_chip structure for
> each PWM it can control. Wouldn't it be easier in such cases to just specify
> how many PWMs a chip wants to register, much like gpiolib does it?

It may be more suitable for some devices like for example the mxs driver
or the at91 driver which Bill has in his tree. However, the idea of this
series was to move the drivers over with the least possible breakage.
Once the drivers are consolidated in a single directory with a single
framework it will be easier to modify.

Sascha