linux-kernel - Re: [PATCH 1/2] PCI: rockchip: Work around missing device

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Message-ID: <87pn7qnabq.wl-maz@kernel.org>
Date:   Sun, 16 Aug 2020 11:39:53 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-pci@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Rob Herring <robh@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Heiko Stuebner <heiko@...ech.de>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Roh Herring <robh+dt@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, kernel-team@...roid.com
Subject: Re: [PATCH 1/2] PCI: rockchip: Work around missing device_type property in DT

On Sun, 16 Aug 2020 00:22:28 +0100,
Bjorn Helgaas <helgaas@...nel.org> wrote:
> 
> On Sat, Aug 15, 2020 at 01:51:11PM +0100, Marc Zyngier wrote:
> > Recent changes to the DT PCI bus parsing made it mandatory for
> > device tree nodes describing a PCI controller to have the
> > 'device_type = "pci"' property for the node to be matched.
> > 
> > Although this follows the letter of the specification, it
> > breaks existing device-trees that have been working fine
> > for years.  Rockchip rk3399-based systems are a prime example
> > of such collateral damage, and have stopped discovering their
> > PCI bus.
> > 
> > In order to paper over the blunder, let's add a workaround
> > to the pcie-rockchip driver, adding the missing property when
> > none is found at boot time. A warning will hopefully nudge the
> > user into updating their DT to a fixed version if they can, but
> > the insentive is obviously pretty small.
> 
> s/insentive/incentive/ (Lorenzo or I can fix this up)
> 
> > Fixes: 2f96593ecc37 ("of_address: Add bus type match for pci ranges parser")
> > Suggested-by: Roh Herring <robh+dt@...nel.org>
> 
> s/Roh/Rob/ (similarly)

Clearly not my day when it comes to proofreading commit messages.
Thanks for pointing this out, and in advance for fixing it up.

> 
> > Signed-off-by: Marc Zyngier <maz@...nel.org>
> 
> This looks like a candidate for v5.9, since 2f96593ecc37 was merged
> during the v5.9 merge window, right?

Absolutely.

> I wonder how many other DTs are similarly broken?  Maybe Rob's DT
> checker has already looked?

I've just managed to run the checker, which comes up with all kinds of
goodies. Apart from the above, it also spots the following:

- arch/arm64/boot/dts/mediatek/mt7622.dtsi: Has a device_type property
  in its main PCIe node, but not in the child nodes. It isn't obvious
  to me whether that's a violation or not (the spec doesn't say
  whether the property should be set on a per-port basis). Rob?

- arch/arm64/boot/dts/qcom/msm8996.dtsi: Only one out of the three
  PCIe nodes has the device_type property, probably broken similarly
  to rk3399.

I could move the workaround to drivers/pci/of.c, and have it called
from the individual drivers. I don't have the HW to test those though.

Thoughts?

	M.

-- 
Without deviation from the norm, progress is not possible.