[PATCH 24/32] pci: PCIe driver for Marvell Armada 370/XP systems

[Thierry Reding]

On Tue, Mar 12, 2013 at 04:08:54PM -0600, Jason Gunthorpe wrote:
> On Tue, Mar 12, 2013 at 10:30:06PM +0100, Thierry Reding wrote:
> 
> > > Not going down the of_pci_* code paths for address translation at the
> > > root port bridge nodes is certainly not right.
> > 
> > I'm not so sure. Why should the pcie-controller be a PCI device?
> 
> The spec is clear on that point as well:
> 
>  device_type
>   A Standard Package conforming to this specification and corresponding
>   to a device that implements a PCI bus shall implement this property
>   with the string value "pci"
> 
> The children of a pcie-controller node are PCI devices, thus the
> pcie-controller node 'implements a PCI bus'. Or, as you say 'device on
> the processor/SoC/platform bus that bridges to the PCI bus'
> 
> Think of device_type as also meaning bus_type and it makes more
> logical sense, the name is terrible, but its usage is governed by the
> OF docs..
> 
> > The other alternative would be to amend the specification. Besides the
> > fact that the specification says so I don't see any reason why this
> > shouldn't be allowed.
> 
> 'the specification says so' *IS* the reason. DT isn't a free for all
> where you get to do whatever you want, or whatever 'feels' right. It
> is supposed to be a stable, OS agnostic ABI. That means bindings have
> to follow the specs (when available).
> 
> Maybe a future revision will support PCI-E ECAM, but we don't know
> what that will look like, and I'm pretty sure you don't want to hold
> up your patches until an IEEE committee gets around to deciding
> something ;)

Mitch already answered this. The specification is now almost 15 years
old and it couldn't possibly have foreseen all of the future use-cases.
If the specification is too restrictive and Mitch gives his blessing to
remove some of the restrictions, I don't see any reason why we shouldn't
do so if it lets us represent the reality of hardware more accurately in
DT.

Furthermore we're not discussing radical changes. None of the changes
will be backwards-incompatible, but they will allow recent hardware to
be represented more correctly or conveniently.

Thierry
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