[PATCH v2 1/2] fsl: Add binding for RCPM

[Wang Dongsheng]

> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Wednesday, September 16, 2015 10:38 AM
> To: Tang Yuantian-B29983
> Cc: Wang Dongsheng-B40534; devicetree at vger.kernel.org; linuxppc-
> dev at lists.ozlabs.org; robh+dt at kernel.org; linux-arm-kernel at lists.infradead.org;
> Wang Huan-B18965; Jin Zhengxiong-R64188; Zhao Chenhui-B35336
> Subject: Re: [PATCH v2 1/2] fsl: Add binding for RCPM
> 
> On Tue, 2015-09-15 at 21:35 -0500, Tang Yuantian-B29983 wrote:
> >
> > > -----Original Message-----
> > > From: Wood Scott-B07421
> > > Sent: Wednesday, September 16, 2015 10:32 AM
> > > To: Wang Dongsheng-B40534 <Dongsheng.Wang at freescale.com>
> > > Cc: devicetree at vger.kernel.org; linuxppc-dev at lists.ozlabs.org;
> > > robh+dt at kernel.org; linux-arm-kernel at lists.infradead.org; Wang Huan-
> > > B18965 <alison.wang at freescale.com>; Jin Zhengxiong-R64188
> > > <Jason.Jin at freescale.com>; Zhao Chenhui-B35336
> > > <chenhui.zhao at freescale.com>; Tang Yuantian-B29983
> > > <Yuantian.Tang at freescale.com>
> > > Subject: Re: [PATCH v2 1/2] fsl: Add binding for RCPM
> > >
> > > On Tue, 2015-09-15 at 21:30 -0500, Wang Dongsheng-B40534 wrote:
> > > > Hi Scott,
> > > >
> > > > > -----Original Message-----
> > > > > From: Wood Scott-B07421
> > > > > Sent: Wednesday, September 16, 2015 10:19 AM
> > > > > To: Wang Dongsheng-B40534
> > > > > Cc: devicetree at vger.kernel.org; linuxppc-dev at lists.ozlabs.org;
> > > > > robh+dt at kernel.org; linux-arm-kernel at lists.infradead.org; Wang Huan-
> > > > > B18965; Jin
> > > > > Zhengxiong-R64188; Zhao Chenhui-B35336; Tang Yuantian-B29983
> > > > > Subject: Re: [PATCH v2 1/2] fsl: Add binding for RCPM
> > > > >
> > > > > On Tue, 2015-09-15 at 21:15 -0500, Wang Dongsheng-B40534 wrote:
> > > > > > Hi Scott,
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Wood Scott-B07421
> > > > > > > Sent: Wednesday, September 16, 2015 7:57 AM
> > > > > > > To: Wang Dongsheng-B40534
> > > > > > > Cc: devicetree at vger.kernel.org; linuxppc-dev at lists.ozlabs.org;
> > > > > > > robh+dt at kernel.org; linux-arm-kernel at lists.infradead.org; Wang
> > > > > > > robh+Huan-
> > > > > > > B18965; Jin
> > > > > > > Zhengxiong-R64188; Zhao Chenhui-B35336; Tang Yuantian-B29983
> > > > > > > Subject: Re: [PATCH v2 1/2] fsl: Add binding for RCPM
> > > > > > >
> > > > > > > On Tue, 2015-09-15 at 16:55 +0800, Dongsheng Wang wrote:
> > > > > > > > +* Freescale RCPM Wakeup Source Device Tree Bindings
> > > > > > > > +-------------------------------------------
> > > > > > > > +Required rcpm-wakeup property should be added to a device
> > > > > > > > +node if the
> > > > > > > > device
> > > > > > > > +can be used as a wakeup source.
> > > > > > > > +
> > > > > > > > +  - rcpm-wakeup: The value of the property consists of 3 cells.
> > > > > > > > + The
> > > > > > > > first
> > > > > > > > cell
> > > > > > > > +     is a pointer to the rcpm node, the second cell is the
> > > > > > > > + bit mask
> > > > > > > > that
> > > > > > > > +     should be set in IPPDEXPCR0, and the last cell is for
> > > > > > > > IPPDEXPCR1.
> > > > > > > > +     Note: If the platform has no IPPDEXPCR1 register, put a
> > > > > > > > + zero
> > > > > > > > here.
> > > > > > >
> > > > > > > What if a future platform has more than two of these registers?
> > > > > >
> > > > > > Those registers are only used for wakeup device, we have a lot of
> > > > > > available bit for feature. For example, In LS1021a platform only
> > > > > > 7bits has used in the registers, and 57bits is reserved.
> > > > >
> > > > > Still, it'd be better to for the rcpm node to advertise the number
> > > > > of cells it expects.
> > > >
> > > > For the foreseeable future it should be enough to use, even if not
> > > > enough to use in the future at that time we can update the binding.
> > >
> > > That's the whole point.  Device tree is stable ABI.  Updating it later to
> > > not be
> > > fixed to two cells would be a lot harder than getting it right from the
> > > beginning.  Putting the number of cells in the phandle target is a
> > > standard
> > > device tree idiom.
> > >
> > I agree with you. But what's the point a SOC has more than 64 wakeup source?
> 
> I don't know.  Hardware people do strange things sometimes.  They might not
> want to reuse bits they once used for something on some other chip, or they
> might have some encoding scheme in mind that results in the bits not being
> packed as tightly as possible, or there may be some big array of similar
> devices...
> 
> What's the point of skipping this part of the phandle-plus-arguments idiom?

Fine, I will add a property in rcpm node to describe the number of register.

Regards,
-Dongsheng