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

Marc Zyngier
2020-08-18T17:35:04Z

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"));
}

static void of_bus_pci_count_cells(struct device_node *np,

It should address all the drivers in one go, and yet tell users
that something is amiss.

M.
--
Jazz is not dead. It just smells funny...