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>

3 files changed, 92 insertions, 0 deletions

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 13d796547ebd..b43e288ec567 100644
--- a/arch/mips/Kconfig.debug
+++ b/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
diff --git a/arch/mips/mm/Makefile b/arch/mips/mm/Makefile
index 67ede4ef9b8d..b4c64bd3f723 100644
--- a/arch/mips/mm/Makefile
+++ b/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
diff --git a/arch/mips/mm/sc-debugfs.c b/arch/mips/mm/sc-debugfs.c
new file mode 100644
index 000000000000..5eefe3281b24
--- /dev/null
+++ b/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);