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Re: [PATCH] xen: workaround missing device_type property in pci/pcie nodes

Hi Stefano,

On 09/02/2021 17:47, Stefano Stabellini wrote:
On Tue, 9 Feb 2021, Bertrand Marquis wrote:
Hi Stefano,

On 8 Feb 2021, at 23:56, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:

PCI buses differ from default buses in a few important ways, so it is
important to detect them properly. Normally, PCI buses are expected to
have the following property:

    device_type = "pci"

In reality, it is not always the case. To handle PCI bus nodes that
don't have the device_type property, also consider the node name: if the
node name is "pcie" or "pci" then consider the bus as a PCI bus.

This commit is based on the Linux kernel commit
d1ac0002dd29 "of: address: Work around missing device_type property in
pcie nodes".

This fixes Xen boot on RPi4.
I am a bit confused with this sentence... How did you manage to boot Xen on RPi4 before hand?

We are really handling here a wrong device-tree bug that could easily be fixed
by the user.
We should at least mention in the commit message that this is a workaround
to solve RPi4 buggy device tree.

Not sure if it can be "easily" fixed by the user -- it took me a few
hours to figure out what the problem was, and I know Xen and device tree
pretty well :-)

Yes it would be good to have a link to the discussion in the commit
message, using the Link tag. It could be done on commit, or I can add it
to the next version.

A summary of the discussion would be useful in the commit message so a reader can easily make the connection between the Linux commit and the Xen one.

Link: https://lore.kernel.org/xen-devel/YBmQQ3Tzu++AadKx@xxxxxxxxxxxxxxxx/

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>

diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c
index 18825e333e..f1a96a3b90 100644
--- a/xen/common/device_tree.c
+++ b/xen/common/device_tree.c
@@ -563,14 +563,28 @@ static unsigned int dt_bus_default_get_flags(const __be32 
  * PCI bus specific translator

+static bool_t dt_node_is_pci(const struct dt_device_node *np)
+    bool is_pci = !strcmp(np->name, "pcie") || !strcmp(np->name, "pci");

The Linux commit is a bit more restrictive and only does that for “pcie”.
Any reason why you also want to have this workaround done also for “pci” ?

Yes, that's because in our case the offending node is named "pci" not
"pcie" so the original Linux commit wouldn't cover it.

+    if (is_pci)
+        printk(XENLOG_WARNING "%s: Missing device_type\n", np->full_name);
+    return is_pci;
static bool_t dt_bus_pci_match(const struct dt_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" or "pci", accept the device as PCI (with a warning).
     return !strcmp(np->type, "pci") || !strcmp(np->type, "pciex") ||
-        !strcmp(np->type, "vci") || !strcmp(np->type, "ht");
+        !strcmp(np->type, "vci") || !strcmp(np->type, "ht") ||
+        dt_node_is_pci(np);

static void dt_bus_pci_count_cells(const struct dt_device_node *np,

Julien Grall



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