[Intel-gfx] Reviving the LPSS PWM patches

[Lluís Batlle i Rossell]

On Sat, Apr 09, 2016 at 11:14:38AM +0200, Lluís Batlle i Rossell wrote:
> On Thu, Apr 07, 2016 at 11:54:39AM +0200, Lluís Batlle i Rossell wrote:
> > On Thu, Apr 07, 2016 at 03:19:04PM +0530, Kumar, Shobhit wrote:
> > > On Wednesday 06 April 2016 04:26 PM, Lluís Batlle i Rossell wrote:
> > > >I don't see any trace of pwm/lpss in dmesg, so it's normal that i915 fails
> > > >to find it. I wonder if there may be a problem in the ACPI table. I have
> > > >the DSDT and it clearly reports the:
> > > >
> > > >Name (_CID, "80860F09")  // _CID: Compatible ID
> > > >Name (_DDN, "Intel(R) PWM Controller #2 - 80860F09")  // _DDN: DOS Device Name
> > > >
> > > >Which should be the lpss pwm. But somehow it is not loaded, so I guess it
> > > >fails the probing.
> > > 
> > > Can we put some prints in the probe routines and see whats happening in the
> > > pwm-lpss-platform.c driver. There is also a PCI PWM LPSS driver -
> > > pwm-lpss-pci.c Can you also enable that and see if the probe for that is
> > > being called and successful ?

I think there is a lot to be done first, to be able to test this.

If I understand correctly, despite the lpss pwm may be available, it will
not be used as pwm-backlight (video/backlight/pwm_bl.c) because it depends
on "CONFIG_OF" and it is ready for devicetree only.

The only x86 that enable OF are X86_INTEL_CE and OLPC, and pwm_bl is
completely disabled without OF. I don't have any INTEL_CE or OLPC, this
LPSS of the Atom SoC is a different thing.

So, someone has to implement pwm_bl on my x86 first, for any of the
patches wrt i915 to be used at all. Should X86_INTEL_LPSS enable OF?
Should there be a devicetree definition for it first? Does someone have to
allow pwm_bl to work with ACPI? Is all that ready in some branch of some
other linux team?

Regards,
Lluís.

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