Hi Will, Mark,

On 2016/3/30 0:31, Mark Rutland wrote:

On Tue, Mar 29, 2016 at 05:18:38PM +0100, Will Deacon wrote:

quoted

quoted

On Thu, Mar 24, 2016 at 10:44:31PM +0800, Shannon Zhao wrote:

quoted

quoted

When it's a Xen domain0 booting with ACPI, it will supply a /chosen and
a /hypervisor node in DT. So check if it needs to enable ACPI.

Signed-off-by: Shannon Zhao <redacted>
Reviewed-by: Stefano Stabellini <redacted>
Acked-by: Hanjun Guo <redacted>
---
 arch/arm64/kernel/acpi.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index d1ce8e2..4e92be0 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c

@@ -67,10 +67,13 @@ static int __init dt_scan_depth1_nodes(unsigned long node,
 {
 	/*
 	 * Return 1 as soon as we encounter a node at depth 1 that is
-	 * not the /chosen node.
+	 * not the /chosen node, or /hypervisor node when running on Xen.
 	 */
-	if (depth == 1 && (strcmp(uname, "chosen") != 0))
-		return 1;
+	if (depth == 1 && (strcmp(uname, "chosen") != 0)) {
+		if (!xen_initial_domain() || (strcmp(uname, "hypervisor") != 0))
+			return 1;
+	}

Hmm, but xen_initial_domain() is false when xen isn't being used at all,
so it feels to me like this is a bit too far-reaching and is basically
claiming the "/hypervisor" namespace for Xen. Couldn't it be renamed to
"xen,hypervisor" or something?

Mark, got any thoughts on this?

The node has a compatible string, "xen,xen" per [1], which would tell us
absolutely that xen is present. I'd be happy checking for that
explicitly.

I think actually the xen_initial_domain is the result of the
fdt_find_hyper_node. If the compatible string "xen,xen" doesn't exist,
the xen_initial_domain() will return false and whatever the current node
is the above check will return 1 since the device tree is not empty.

In patch 11 fdt_find_hyper_node checks the compatible string. We could
factor that out into a helper like is_xen_node(node) and use it here
too.

I don't think so because we already check the compatible string before
and we could get the result simply via xen_initial_domain().

Thanks,
-- 
Shannon