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

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Date:   Fri, 14 Aug 2020 19:21:31 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>
Cc:     linux-mips@...r.kernel.org, Rob Herring <robh@...nel.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,
        kernel-team@...roid.com
Subject: Re: [PATCH v4 1/5] of_address: Add bus type match for pci ranges
 parser

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.

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).

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.
  	 */
  	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") ||
+		of_find_property(np, "linux,pci-domain", NULL);
  }

  static void of_bus_pci_count_cells(struct device_node *np,
-- 
2.27.0

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