MIPS: Allow L2 prefetch to be configured via debugfs

When debugging or examining the performance of a system it can be useful
to examine the effect of L2 prefetching. Provide an optional debugfs
entry to allow a user to enable or disable L2 prefetching.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11182/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig.debug

@@ -149,4 +149,14 @@ endchoice
 
 endif # CPU_MIPSR6
 
+config SCACHE_DEBUGFS
+	bool "L2 cache debugfs entries"
+	depends on DEBUG_FS
+	help
+	  Enable this to allow parts of the L2 cache configuration, such as
+	  whether or not prefetching is enabled, to be exposed to userland
+	  via debugfs.
+
+	  If unsure, say N.
+
 endmenu

arch/mips/mm/Makefile

@@ -28,3 +28,4 @@ obj-$(CONFIG_IP22_CPU_SCACHE)	+= sc-ip22.o
 obj-$(CONFIG_R5000_CPU_SCACHE)	+= sc-r5k.o
 obj-$(CONFIG_RM7000_CPU_SCACHE) += sc-rm7k.o
 obj-$(CONFIG_MIPS_CPU_SCACHE)	+= sc-mips.o
+obj-$(CONFIG_SCACHE_DEBUGFS)	+= sc-debugfs.o

arch/mips/mm/sc-debugfs.c

@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2015 Imagination Technologies
+ * Author: Paul Burton <paul.burton@imgtec.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ */
+
+#include <asm/bcache.h>
+#include <asm/debug.h>
+#include <asm/uaccess.h>
+#include <linux/debugfs.h>
+#include <linux/init.h>
+
+static ssize_t sc_prefetch_read(struct file *file, char __user *user_buf,
+				size_t count, loff_t *ppos)
+{
+	bool enabled = bc_prefetch_is_enabled();
+	char buf[3];
+
+	buf[0] = enabled ? 'Y' : 'N';
+	buf[1] = '\n';
+	buf[2] = 0;
+
+	return simple_read_from_buffer(user_buf, count, ppos, buf, 2);
+}
+
+static ssize_t sc_prefetch_write(struct file *file,
+				 const char __user *user_buf,
+				 size_t count, loff_t *ppos)
+{
+	char buf[32];
+	ssize_t buf_size;
+	bool enabled;
+	int err;
+
+	buf_size = min(count, sizeof(buf) - 1);
+	if (copy_from_user(buf, user_buf, buf_size))
+		return -EFAULT;
+
+	buf[buf_size] = '\0';
+	err = strtobool(buf, &enabled);
+	if (err)
+		return err;
+
+	if (enabled)
+		bc_prefetch_enable();
+	else
+		bc_prefetch_disable();
+
+	return count;
+}
+
+static const struct file_operations sc_prefetch_fops = {
+	.open = simple_open,
+	.llseek = default_llseek,
+	.read = sc_prefetch_read,
+	.write = sc_prefetch_write,
+};
+
+static int __init sc_debugfs_init(void)
+{
+	struct dentry *dir, *file;
+
+	if (!mips_debugfs_dir)
+		return -ENODEV;
+
+	dir = debugfs_create_dir("l2cache", mips_debugfs_dir);
+	if (IS_ERR(dir))
+		return PTR_ERR(dir);
+
+	file = debugfs_create_file("prefetch", S_IRUGO | S_IWUSR, dir,
+				   NULL, &sc_prefetch_fops);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	return 0;
+}
+late_initcall(sc_debugfs_init);