[RFC] powerpc/fsl-pci: Document the "fsl,has-isa" property for Freescale PCI

[Jia Hongtao-B38951]

> -----Original Message-----
> From: linuxppc-dev-bounces+b38951=freescale.com at lists.ozlabs.org
> [mailto:linuxppc-dev-bounces+b38951=freescale.com at lists.ozlabs.org] On
> Behalf Of Jia Hongtao-B38951
> Sent: Friday, April 06, 2012 11:05 AM
> To: Kumar Gala
> Cc: devicetree-discuss at lists.ozlabs.org; linuxppc-dev at lists.ozlabs.org;
> Li Yang-R58472
> Subject: RE: [RFC] powerpc/fsl-pci: Document the "fsl,has-isa" property
> for Freescale PCI
> 
> 
> > -----Original Message-----
> > From: Kumar Gala [mailto:galak at kernel.crashing.org]
> > Sent: Wednesday, April 04, 2012 9:09 PM
> > To: Jia Hongtao-B38951
> > Cc: linuxppc-dev at lists.ozlabs.org; Li Yang-R58472; devicetree-
> > discuss at lists.ozlabs.org
> > Subject: Re: [RFC] powerpc/fsl-pci: Document the "fsl,has-isa" property
> > for Freescale PCI
> >
> >
> > On Apr 1, 2012, at 1:56 AM, Jia Hongtao wrote:
> >
> > > If PCI is primary bus we should set isa_io/mem_base when parsing PCI
> > bridge
> > > resources from device tree. The previous way to check the primary bus
> > based
> > > on a hard-coded address named primary_phb_addr. Now we add a property
> > named
> > > "fsl,has-isa" into device tree. In kernel we use this property to
> find
> > out
> > > the bus is primary or not. This way is more flexible.
> > >
> > > Signed-off-by: Jia Hongtao <B38951 at freescale.com>
> > > Signed-off-by: Li Yang <leoli at freescale.com>
> > > ---
> > > .../devicetree/bindings/powerpc/fsl/pci.txt        |   36
> > ++++++++++++++++++++
> > > 1 files changed, 36 insertions(+), 0 deletions(-)
> > > create mode 100644
> > Documentation/devicetree/bindings/powerpc/fsl/pci.txt
> >
> > This isn't freescale specific, its linux specific.  If anything the
> > property should be linux,has-isa.
> >
> > But in general I dont think this is a good idea.  In truth one could
> > search the device tree for:
> >
> > 	device_type = "isa";
> >
> > to try and set this dynamically.
> >
> > - k
> >
> 
> Yes, it's not Freescale specific, but it's only used by Freescale now in
> the kernel. This is why I named the property as "fsl,has-isa".
> 
> To indicate PCI bus is primary we have three ways to go and we now like
> the 2nd solution:
> 
> 1. As this patch said, we add a property to device tree manually.
> 
> 2. Set this property dynamically in uboot when scanning PCI bridge.
> Actually we have already done this. The problem is users should update
> uboot and kernel together or it's not work. To support old uboot we
> decide
> to add this property into device tree too temporarily. We will remove it
> from device tree at an appropriate future.
> 
> 3. Just as you said we could search the device tree by device_type =
> "isa".
>    There are two problems here:
> 	* There is no OF API for searching just in PCI node now. That means
> 	  we can't easily find whether there is "isa" bridge or not under
> 	  this PCI controller while scanning it.
> 	* Boards MPC8541CDS and MPC8555CDS has no "isa" node in device tree
> 	  but has ISA bridge under PCI controller.
> 
> - Jia Hongtao
> 

Hi Kumar,

I agree with the name change from "fsl,has-isa" to "linux,has-isa".
If this is ok I will update this patch and send the patches based on this
new property.

Also, I have a question about "isa" node in dts. Is this node being used
by kernel? If not we can remove it from all boards and check the primary
bus by uboot. If "isa" is useful why MPC8541CDS and MPC8555CDS has no
"isa" node in device tree but has ISA bridge under PCI controller?

Thanks.
- Jia Hongtao