Re: [PATCH 1/2] PCI: rockchip: Work around missing device_type property in DT

Saravana Kannan
2020-08-18T17:49:35Z

On Tue, Aug 18, 2020 at 10:34 AM Marc Zyngier <maz@kernel.org> wrote:
>
> On 2020-08-18 15:23, Rob Herring wrote:
> > On Tue, Aug 18, 2020 at 1:35 AM Marc Zyngier <maz@kernel.org> wrote:
> >>
> >> On 2020-08-17 17:12, Rob Herring wrote:
> >> > On Sun, Aug 16, 2020 at 4:40 AM Marc Zyngier <maz@kernel.org> wrote:
> >> >>
> >> >> On Sun, 16 Aug 2020 00:22:28 +0100,
> >> >> Bjorn Helgaas <helgaas@kernel.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@kernel.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@kernel.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?
> >> >
> >> > The rule is bridge nodes should have 'device_type = "pci"'. But what's
> >> > needed to fix these cases is setting device_type where we are parsing
> >> > ranges or dma-ranges which we're not doing on the child ndes.
> >> > Otherwise, I don't think it matters in this case unless you have child
> >> > (grandchild here) nodes for PCI devices. If you did have child nodes,
> >> > the address translation was already broken before this change.
> >>
> >> Fair enough.
> >>
> >> >> - 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.
> >> >
> >> > The only upstream board is DB820c, so probably not as wide an impact...
> >> >
> >> > There are also 92 (lots of duplicates due to multiple boards) more
> >> > cases in arch/arm/. A log is here[1].
> >>
> >> Mostly Broadcom stuff, apparently. I'll see if I can have a stab
> >> at it (although someone will have to test it).
> >>
> >> >
> >> >> 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?
> >> >
> >> > I think we should go with my other suggestion of looking at the node
> >> > name. Looks like just checking 'pcie' is enough. We can skip 'pci' as
> >> > I don't see any cases.
> >>
> >> I really dislike it.
> >>
> >> Once we put this node name matching in, there is no incentive for
> >> people to write their DT correctly at all. It also sound pretty
> >> fragile (what if the PCIe node is named something else?).
> >
> > That would require 2 wrongs. Both missing device_type and wrong node
> > name. You could still warn if we matched on node name.
>
> OK. So how about something like this?
>
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index 590493e04b01..a7a6ee599b14 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -134,9 +134,13 @@ static int of_bus_pci_match(struct device_node *np)
> * "pciex" is PCI Express
> * "vci" is for the /chaos bridge on 1st-gen PCI powermacs
> * "ht" is hypertransport
> + *
> + * If none of the device_type match, and that the node name is
> + * "pcie", accept the device as PCI (with a warning).
> */
> return of_node_is_type(np, "pci") || of_node_is_type(np, "pciex") ||
> - of_node_is_type(np, "vci") || of_node_is_type(np, "ht");
> + of_node_is_type(np, "vci") || of_node_is_type(np, "ht") ||
> + WARN_ON_ONCE(of_node_name_eq(np, "pcie"));

I don't think we need the _ONCE. Otherwise, it'd warn only for the
first device that has this problem.

How about?
WARN(of_node_name_eq(np, "pcie"), "Missing device type in %pOF", np)

That'll even tell them which node is bad.

-Saravana