linux-kernel - Re: [PATCH v4 1/5] of_address: Add bus type match for pci ranges parser

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Message-ID: <34ac2d7c0770f9aa450aaa3905c82f52@kernel.org>
Date:   Sat, 15 Aug 2020 12:22:41 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Jiaxun Yang <jiaxun.yang@...goat.com>,
        Frank Rowand <frowand.list@...il.com>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhc@...ote.com>,
        Paul Burton <paulburton@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH v4 1/5] of_address: Add bus type match for pci ranges
 parser

On 2020-08-14 23:51, Rob Herring wrote:
> On Fri, Aug 14, 2020 at 12:21 PM Marc Zyngier <maz@...nel.org> wrote:
>> 
>> Hi all,
>> 
>> On 2020-07-28 16:36, Jiaxun Yang wrote:
>> > So the parser can be used to parse range property of ISA bus.
>> >
>> > As they're all using PCI-like method of range property, there is no
>> > need
>> > start a new parser.
>> >
>> > Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
>> > Reviewed-by: Rob Herring <robh@...nel.org>
>> 
>> This patch, although it looks correct, breaks the RK3399-based
>> systems, as they miss the (now required) 'device_type = "pci";'
>> property.
> 
> Required since 1990 something...

And yet... The fact that it has been broken from day-1 (3.5 years
ago) shows how good we are at enforcing those requirements.

> 
>> We can fix the in-tree DT, but that's not really an option
>> if someone relies on the DT being provided by the firmware
>> (I for one definitely do).
> 
> Perhaps time to pay attention to schema errors:
> 
> arch/arm64/boot/dts/rockchip/rk3399-sapphire-excavator.dt.yaml:
> pcie@...00000: 'device_type' is a required property

As long as this isn't part of the normal build flow, these errors
will get ignored. I don't even know how to trigger this validation,
TBH.

> (I thought dtc would also catch this, but there we look for
> device_type and then do PCI checks like node name. I guess we needed
> to check for either device_type or the node name...)

That would be much better. At least this *does* run at build time.

> 
>> I came up with the following hack, which solves the issue for
>> me. Definitely not my finest hour, but I really need this box
>> to keep going. I will post a patch fixing the DT separately.
>> 
>> Thanks,
>> 
>>          M.
>> 
>>  From ceef5fd9c4d2005eb577505c68868ebe527c098f Mon Sep 17 00:00:00 
>> 2001
>>  From: Marc Zyngier <maz@...nel.org>
>> Date: Fri, 14 Aug 2020 19:10:12 +0100
>> Subject: [PATCH] of: address: Workaround broken DTs missing the
>> 'device_type =
>>   "pci"' property
>> 
>> Recent changes to the PCI bus parsing made it mandatory for
>> device trees nodes describing a PCI controller to have the
>> 'device_type = "pci"' property for the node to be matched.
>> 
>> Although this is compliant with the specification, it breaks
>> existing device-trees that have been working fine for years
>> (the Rockchip rk3399-based systems being a prime example of
>> such breakage).
>> 
>> In order to paper over the blunder, let's also match nodes
>> that have the "linux,pci-domain" property, as they are
>> pretty likely to be PCI nodes. This fixes the issue for
>> systems such as the above platforms.
>> 
>> Fixes: 2f96593ecc37 ("of_address: Add bus type match for pci ranges
>> parser")
>> Signed-off-by: Marc Zyngier <maz@...nel.org>
>> ---
>>   drivers/of/address.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/of/address.c b/drivers/of/address.c
>> index 590493e04b01..712e03781a2a 100644
>> --- a/drivers/of/address.c
>> +++ b/drivers/of/address.c
>> @@ -134,9 +134,12 @@ 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
>> +        * "linux,pci-domain" is a workaround for broken device trees
>> +        * lacking the required "device_type" property.
> 
> I would suggest looking for 'pci' or 'pcie' node name instead.
> 
> You should remove linux,pci-domain from rk3399 as it is pointless when
> there's a single PCI host bridge.

Indeed. I was clutching at straws here.

> 
> The other option is fixup the live tree with of_add_property() in the
> Rockchip PCI driver. Less likely to impact anyone else.

That's actually a much better solution, thanks for pointing this out.
At least I can shout about broken DTs while fixing it up, and the
new fix is fairly neat.

I'll post new patches shortly.

Thanks,

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