linux-kernel - [PATCH v2 1/3] drivers/of: recognize status property of dt memory nodes

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Date:   Wed, 14 Sep 2016 15:06:56 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Bharata B Rao <bharata@...ux.vnet.ibm.com>,
        Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Alistair Popple <apopple@....ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, devicetree@...r.kernel.org,
        linux-mm@...ck.org
Subject: [PATCH v2 1/3] drivers/of: recognize status property of dt memory nodes

Respect the standard dt "status" property when scanning memory nodes in
early_init_dt_scan_memory(), so that if the property is present and not
"okay", no memory will be added.

The use case at hand is accelerator or device memory, which may be
unusable until post-boot initialization of the memory link. Such a node
can be described in the dt as any other, given its status is "disabled".
Per the device tree specification,

"disabled"
	Indicates that the device is not presently operational, but it
	might become operational in the future (for example, something
	is not plugged in, or switched off).

Once such memory is made operational, it can then be hotplugged.

Signed-off-by: Reza Arbab <arbab@...ux.vnet.ibm.com>
---
 drivers/of/fdt.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 085c638..fc19590 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -1022,8 +1022,10 @@ int __init early_init_dt_scan_memory(unsigned long node, const char *uname,
 				     int depth, void *data)
 {
 	const char *type = of_get_flat_dt_prop(node, "device_type", NULL);
+	const char *status;
 	const __be32 *reg, *endp;
 	int l;
+	bool add_memory;
 
 	/* We are scanning "memory" nodes only */
 	if (type == NULL) {
@@ -1044,6 +1046,9 @@ int __init early_init_dt_scan_memory(unsigned long node, const char *uname,
 
 	endp = reg + (l / sizeof(__be32));
 
+	status = of_get_flat_dt_prop(node, "status", NULL);
+	add_memory = !status || !strcmp(status, "okay");
+
 	pr_debug("memory scan node %s, reg size %d,\n", uname, l);
 
 	while ((endp - reg) >= (dt_root_addr_cells + dt_root_size_cells)) {
@@ -1057,6 +1062,9 @@ int __init early_init_dt_scan_memory(unsigned long node, const char *uname,
 		pr_debug(" - %llx ,  %llx\n", (unsigned long long)base,
 		    (unsigned long long)size);
 
+		if (!add_memory)
+			continue;
+
 		early_init_dt_add_memory_arch(base, size);
 	}
 
-- 
1.8.3.1