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From: Heiko =?ISO-8859-1?Q?St=FCbner?= <heiko@sntech.de>
To: Rob Herring <robh@kernel.org>, Niklas Cassel <Niklas.Cassel@wdc.com>
Cc: Niklas Cassel <nks@flawful.org>,
 Lorenzo Pieralisi <lpieralisi@kernel.org>,
 Krzysztof =?utf-8?B?V2lsY3p5xYRza2k=?= <kw@linux.com>,
 Bjorn Helgaas <bhelgaas@google.com>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
 Conor Dooley <conor+dt@kernel.org>, Shawn Lin <shawn.lin@rock-chips.com>,
 Simon Xue <xxm@rock-chips.com>, Damien Le Moal <dlemoal@kernel.org>,
 Sebastian Reichel <sebastian.reichel@collabora.com>,
 Serge Semin <fancer.lancer@gmail.com>,
 "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
 "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
 "linux-arm-kernel@lists.infradead.org"
 <linux-arm-kernel@lists.infradead.org>,
 "linux-rockchip@lists.infradead.org" <linux-rockchip@lists.infradead.org>
Subject:
 Re: [PATCH v3 1/6] dt-bindings: PCI: dwc: rockchip: Add mandatory atu reg
Date: Fri, 27 Oct 2023 19:07:00 +0200
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Hi Niklas,

Am Freitag, 27. Oktober 2023, 18:14:32 CEST schrieb Niklas Cassel:
> On Fri, Oct 27, 2023 at 10:58:28AM -0500, Rob Herring wrote:
> > On Fri, Oct 27, 2023 at 9:56=E2=80=AFAM Niklas Cassel <nks@flawful.org>=
 wrote:
> > >
> > > From: Niklas Cassel <niklas.cassel@wdc.com>
> > >
> > > Even though rockchip-dw-pcie.yaml inherits snps,dw-pcie.yaml
> > > using:
> > >
> > > allOf:
> > >   - $ref: /schemas/pci/snps,dw-pcie.yaml#
> > >
> > > and snps,dw-pcie.yaml does have the atu reg defined, in order to be
> > > able to use this reg, while still making sure 'make CHECK_DTBS=3Dy'
> > > pass, we need to add this reg to rockchip-dw-pcie.yaml.
> > >
> > > All compatible strings (rockchip,rk3568-pcie and rockchip,rk3588-pcie)
> > > should have this reg.
> > >
> > > The regs in the example are updated to actually match pcie3x2 on rk35=
68.
> >=20
> > Breaking compatibility on these platforms is okay because ...?
>=20
> I don't follow, could you please elaborate?

you're adding the atu reg unconditionally as required element.

Newer kernel versions (strongly) _should_ work with older devicetrees.
So a kernel with that change should also work with a dtb build from the
old style.

DTBs are essentially part of the device firmware, so while some devices
can update theirs easily, you can't really require a dtb update.

I guess you could something like:

   reg-names:
     oneOf:
       - deprecated: true
         items:
         - const: dbi
         - const: apb
         - const: config
       - items:
         - const: dbi
         - const: apb
         - const: config
         - const: atu
=20
(may not be accurate and to spec yet)