Re: [PATCH dt + pci 1/2] dt-bindings: Add 'slot-power-limit-milliwatt' PCIe port property

["Marek Behún" <kabel@kernel.org>]

On Fri, 12 Nov 2021 18:12:49 +0100
Pali Rohár <pali@kernel.org> wrote:

> On Friday 12 November 2021 10:30:01 Rob Herring wrote:
> > On Fri, Nov 12, 2021 at 9:32 AM Pali Rohár <pali@kernel.org> wrote:  
> > >
> > > On Friday 12 November 2021 09:25:20 Rob Herring wrote:  
> > > > On Sun, Oct 31, 2021 at 04:07:05PM +0100, Marek Behún wrote:  
> > > > > +   If present, this property specifies slot power limit in milliwatts. Host
> > > > > +   drivers can parse this property and use it for programming Root Port or host
> > > > > +   bridge, or for composing and sending PCIe Set_Slot_Power_Limit messages
> > > > > +   through the Root Port or host bridge when transitioning PCIe link from a
> > > > > +   non-DL_Up Status to a DL_Up Status.  
> > > >
> > > > If your slots are behind a switch, then doesn't this apply to any bridge
> > > > port?  
> > >
> > > The main issue here is that pci.txt (and also scheme on github) is
> > > mixing host bridge and root ports into one node. This new property
> > > should be defined at the same place where is supports-clkreq or
> > > reset-gpios, as it belongs to them.  
> > 
> > Unfortunately that ship has already sailed. So we can split things up,
> > but we still have to allow for the existing cases. I'm happy to take
> > changes splitting up pci-bus.yaml to 2 or 3 schemas (host bridge,
> > root-port, and PCI(e)-PCI(e) bridge?).  
> 
> Well, no problem. I just need to know how you want to handle backward
> compatibility definitions in YAML. Because it is possible via versioning
> (like in JSONSchema-like structures in OpenAPI versioning) or via
> deprecated attributes or via defining two schemas (one strict and one
> loose)... There are lot of options and I saw all these options in
> different projects which use YAML or JSON.
> 
> I did not know about github repository, I always looked at schemas and
> definitions only in linux kernel tree and external files which were
> mentioned in kernel tree.
> 
> Something I wrote in my RFC email, but I wrote this email patch...
> https://lore.kernel.org/linux-pci/20211023144252.z7ou2l2tvm6cvtf7@pali/

New kernel should always work with old device-tree. But does also new
device-tree need to work with old kernels?

Marek