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From:   Peter Geis <pgwipeout@gmail.com>
Date:   Mon, 18 Apr 2022 12:17:31 -0400
Message-ID: <CAMdYzYpydGyQZT2n9Tf+ccQMLHzfhOgoyamMgspQDcjzm3Umdg@mail.gmail.com>
Subject: Re: Re: [RFC/RFT 4/6] PCI: rockchip-dwc: add pcie bifurcation
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     Frank Wunderlich <frank-w@public-files.de>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Wunderlich <linux@fw-web.de>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        Vinod Koul <vkoul@kernel.org>,
        Krzysztof Kozlowski <krzk+dt@kernel.org>,
        Heiko Stuebner <heiko@sntech.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        =?UTF-8?Q?Krzysztof_Wilczy=C5=84ski?= <kw@linux.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Johan Jonker <jbx6244@gmail.com>,
        Michael Riesch <michael.riesch@wolfvision.net>,
        "open list:GENERIC PHY FRAMEWORK" <linux-phy@lists.infradead.org>,
        devicetree <devicetree@vger.kernel.org>,
        arm-mail-list <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        PCI <linux-pci@vger.kernel.org>
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On Mon, Apr 18, 2022 at 11:53 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Sun, Apr 17, 2022 at 11:08:02AM +0200, Frank Wunderlich wrote:
> > > On Sat, Apr 16, 2022 at 03:54:56PM +0200, Frank Wunderlich wrote:
> > > > From: Frank Wunderlich <frank-w@public-files.de>
> > > >
> > > > PCIe Lanes can be split to 2 slots with bifurcation.
> > > > Add support for this in existing pcie driver.
>
> > > Is the "rockchip,bifurcation" DT property something that should be
> > > generalized so it's not rockchip-specific?  Other controllers are
> > > likely to support similar functionality.
> >
> > I do not know if other controllers support similar functionality,
> > but i ack a property without vendor prefix is better. Should i use
> > "bifurcation" as name or do you think about a different name which
> > is more generic?
>
> Really a question for Rob about what name would be good and where it
> should go.

It might be good to define this as a lane map.
In the Rockchip implementation it's only 2+0 or 1+1, but that isn't
guaranteed if this is made into a standard definition.
So perhaps:
pcie-bifurcation-map = <0>, <1>;
pcie-bifurcation-map = <1>;
pcie-bifurcation-map = <4>, <5>, <6>, <7>;