[PATCH 08/10] powerpc/xive: take into account '/ibm, plat-res-int-priorities'

["Cédric Le Goater" <clg@kaod.org>]

'/ibm,plat-res-int-priorities' contains a list of priorities that the
hypervisor has reserved for its own use. Scan these ranges to choose
the lowest unused priority for the xive spapr backend.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 arch/powerpc/sysdev/xive/spapr.c | 62 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 61 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/sysdev/xive/spapr.c b/arch/powerpc/sysdev/xive/spapr.c
index 7fc40047c23d..220331986bd8 100644
--- a/arch/powerpc/sysdev/xive/spapr.c
+++ b/arch/powerpc/sysdev/xive/spapr.c
@@ -532,13 +532,70 @@ static const struct xive_ops xive_spapr_ops = {
 	.name			= "spapr",
 };
 
+/*
+ * get max priority from "/ibm,plat-res-int-priorities"
+ */
+static bool xive_get_max_prio(u8 *max_prio)
+{
+	struct device_node *rootdn;
+	const __be32 *reg;
+	u32 len;
+	int prio, found;
+
+	rootdn = of_find_node_by_path("/");
+	if (!rootdn) {
+		pr_err("not root node found !\n");
+		return false;
+	}
+
+	reg = of_get_property(rootdn, "ibm,plat-res-int-priorities", &len);
+	if (!reg) {
+		pr_err("Failed to read 'ibm,plat-res-int-priorities' property\n");
+		return false;
+	}
+
+	if (len % (2 * sizeof(u32)) != 0) {
+		pr_err("invalid 'ibm,plat-res-int-priorities' property\n");
+		return false;
+	}
+
+	/* HW supports priorities in the range [0-7] and 0xFF is a
+	 * wildcard priority used to mask. We scan the ranges reserved
+	 * by the hypervisor to find the lowest priority we can use.
+	 */
+	found = 0xFF;
+	for (prio = 0; prio < 8; prio++) {
+		int reserved = 0;
+		int i;
+
+		for (i = 0; i < len / (2 * sizeof(u32)); i++) {
+			int base  = be32_to_cpu(reg[2 * i]);
+			int range = be32_to_cpu(reg[2 * i + 1]);
+
+			if (prio >= base && prio < base + range)
+				reserved++;
+		}
+
+		if (!reserved)
+			found = prio;
+	}
+
+	if (found == 0xFF) {
+		pr_err("no valid priority found in 'ibm,plat-res-int-priorities'\n");
+		return false;
+	}
+
+	*max_prio = found;
+	return true;
+}
+
 bool xive_spapr_init(void)
 {
 	struct device_node *np;
 	struct resource r;
 	void __iomem *tima;
 	struct property *prop;
-	u8 max_prio = 7;
+	u8 max_prio;
 	u32 val;
 	u32 len;
 	const __be32 *reg;
@@ -566,6 +623,9 @@ bool xive_spapr_init(void)
 		return false;
 	}
 
+	if (!xive_get_max_prio(&max_prio))
+		return false;
+
 	/* Feed the IRQ number allocator with the ranges given in the DT */
 	reg = of_get_property(np, "ibm,xive-lisn-ranges", &len);
 	if (!reg) {
-- 
2.7.5