Add kernel 5.15 for RPI4 support

root/target/linux/bcm27xx/patches-5.15/0170-clk-bcm2835-Avoid-null-pointer-exception.patch

@@ -0,0 +1,34 @@
+From 46593228b86c066260d738ae2403562209750374 Mon Sep 17 00:00:00 2001
+From: popcornmix <popcornmix@gmail.com>
+Date: Tue, 6 Aug 2019 15:23:14 +0100
+Subject: [PATCH 170/634] clk-bcm2835: Avoid null pointer exception
+
+clk_desc_array[BCM2835_PLLB] doesn't exist so we dereference null when iterating
+
+Signed-off-by: popcornmix <popcornmix@gmail.com>
+---
+ drivers/clk/bcm/clk-bcm2835.c | 8 +++++---
+ 1 file changed, 5 insertions(+), 3 deletions(-)
+
+diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
+index 857a8e16d014..fe005f9dbe02 100644
+--- a/drivers/clk/bcm/clk-bcm2835.c
++++ b/drivers/clk/bcm/clk-bcm2835.c
+@@ -2304,9 +2304,11 @@ static bool bcm2835_clk_is_claimed(const char *name)
+ 	int i;
+ 
+ 	for (i = 0; i < ARRAY_SIZE(clk_desc_array); i++) {
+-		const char *clk_name = *(const char **)(clk_desc_array[i].data);
+-		if (!strcmp(name, clk_name))
+-		    return bcm2835_clk_claimed[i];
++		if (clk_desc_array[i].data) {
++			const char *clk_name = *(const char **)(clk_desc_array[i].data);
++			if (!strcmp(name, clk_name))
++				return bcm2835_clk_claimed[i];
++		}
+ 	}
+ 
+ 	return false;
+-- 
+2.33.1
+