MIPS: Add debugfs file to print the segmentation control registers

Add a new mips/segments debugfs file to print the 6 segmentation
control registers for supported cores. A sample from a proAptiv core
is given below:
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/6137/
Segment   Virtual    Size   Access Mode   Physical   Caching   EU
-------   -------    ----   -----------   --------   -------   --
   0      e0000000   512M      MK           UND         U       0
   1      c0000000   512M      MSK          UND         U       0
   2      a0000000   512M      UK           000         2       0
   3      80000000   512M      UK           000         3       0
   4      40000000    1G       MUSK         UND         U       1
   5      00000000    1G       MUSK         UND         U       1
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>

arch/mips/kernel/Makefile

@@ -30,6 +30,7 @@ obj-$(CONFIG_CSRC_R4K)		+= csrc-r4k.o
 obj-$(CONFIG_CSRC_SB1250)	+= csrc-sb1250.o
 obj-$(CONFIG_SYNC_R4K)		+= sync-r4k.o
 
+obj-$(CONFIG_DEBUG_FS)		+= segment.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 obj-$(CONFIG_MODULES)		+= mips_ksyms.o module.o
 obj-$(CONFIG_MODULES_USE_ELF_RELA) += module-rela.o

arch/mips/kernel/segment.c

+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2013 Imagination Technologies Ltd.
+ */
+
+#include <linux/kernel.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <asm/cpu.h>
+#include <asm/mipsregs.h>
+
+static void build_segment_config(char *str, unsigned int cfg)
+{
+	unsigned int am;
+	static const char * const am_str[] = {
+		"UK", "MK", "MSK", "MUSK", "MUSUK", "USK",
+		"RSRVD", "UUSK"};
+
+	/* Segment access mode. */
+	am = (cfg & MIPS_SEGCFG_AM) >> MIPS_SEGCFG_AM_SHIFT;
+	str += sprintf(str, "%-5s", am_str[am]);
+
+	/*
+	 * Access modes MK, MSK and MUSK are mapped segments. Therefore
+	 * there is no direct physical address mapping.
+	 */
+	if ((am == 0) || (am > 3)) {
+		str += sprintf(str, "         %03lx",
+			((cfg & MIPS_SEGCFG_PA) >> MIPS_SEGCFG_PA_SHIFT));
+		str += sprintf(str, "         %01ld",
+			((cfg & MIPS_SEGCFG_C) >> MIPS_SEGCFG_C_SHIFT));
+	} else {
+		str += sprintf(str, "         UND");
+		str += sprintf(str, "         U");
+	}
+
+	/* Exception configuration. */
+	str += sprintf(str, "       %01ld\n",
+		((cfg & MIPS_SEGCFG_EU) >> MIPS_SEGCFG_EU_SHIFT));
+}
+
+static int show_segments(struct seq_file *m, void *v)
+{
+	unsigned int segcfg;
+	char str[42];
+
+	seq_puts(m, "Segment   Virtual    Size   Access Mode   Physical   Caching   EU\n");
+	seq_puts(m, "-------   -------    ----   -----------   --------   -------   --\n");
+
+	segcfg = read_c0_segctl0();
+	build_segment_config(str, segcfg);
+	seq_printf(m, "   0      e0000000   512M      %s", str);
+
+	segcfg >>= 16;
+	build_segment_config(str, segcfg);
+	seq_printf(m, "   1      c0000000   512M      %s", str);
+
+	segcfg = read_c0_segctl1();
+	build_segment_config(str, segcfg);
+	seq_printf(m, "   2      a0000000   512M      %s", str);
+
+	segcfg >>= 16;
+	build_segment_config(str, segcfg);
+	seq_printf(m, "   3      80000000   512M      %s", str);
+
+	segcfg = read_c0_segctl2();
+	build_segment_config(str, segcfg);
+	seq_printf(m, "   4      40000000    1G       %s", str);
+
+	segcfg >>= 16;
+	build_segment_config(str, segcfg);
+	seq_printf(m, "   5      00000000    1G       %s\n", str);
+
+	return 0;
+}
+
+static int segments_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, show_segments, NULL);
+}
+
+static const struct file_operations segments_fops = {
+	.open		= segments_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static int __init segments_info(void)
+{
+	extern struct dentry *mips_debugfs_dir;
+	struct dentry *segments;
+
+	if (cpu_has_segments) {
+		if (!mips_debugfs_dir)
+			return -ENODEV;
+
+		segments = debugfs_create_file("segments", S_IRUGO,
+					       mips_debugfs_dir, NULL,
+					       &segments_fops);
+		if (!segments)
+			return -ENOMEM;
+	}
+	return 0;
+}
+
+device_initcall(segments_info);