arm64: add helper functions to read I-cache attributes

This adds helper functions and #defines to <asm/cachetype.h> to read the
line size and the number of sets from the level 1 instruction cache.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/cpuinfo.c

@@ -20,8 +20,10 @@
 #include <asm/cputype.h>
 
 #include <linux/bitops.h>
+#include <linux/bug.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <linux/preempt.h>
 #include <linux/printk.h>
 #include <linux/smp.h>
 
@@ -190,3 +192,15 @@ void __init cpuinfo_store_boot_cpu(void)
 
 	boot_cpu_data = *info;
 }
+
+u64 __attribute_const__ icache_get_ccsidr(void)
+{
+	u64 ccsidr;
+
+	WARN_ON(preemptible());
+
+	/* Select L1 I-cache and read its size ID register */
+	asm("msr csselr_el1, %1; isb; mrs %0, ccsidr_el1"
+	    : "=r"(ccsidr) : "r"(1L));
+	return ccsidr;
+}