firmware: dmi_scan: add SBMIOS entry and DMI tables

Some utils, like dmidecode and smbios, need to access SMBIOS entry
table area in order to get information like SMBIOS version, size, etc.
Currently it's done via /dev/mem. But for situation when /dev/mem
usage is disabled, the utils have to use dmi sysfs instead, which
doesn't represent SMBIOS entry and adds code/delay redundancy when direct
access for table is needed.

So this patch creates dmi/tables and adds SMBIOS entry point to allow
utils in question to work correctly without /dev/mem. Also patch adds
raw dmi table to simplify dmi table processing in user space, as
proposed by Jean Delvare.

Tested-by: Roy Franz <[e-mail]>
Signed-off-by: Ivan Khoronzhuk <[e-mail]>
Signed-off-by: Jean Delvare <[e-mail]>

Documentation/ABI/testing/sysfs-firmware-dmi-tables

···
+What:		/sys/firmware/dmi/tables/
+Date:		April 2015
+Contact:	Ivan Khoronzhuk <[e-mail]>
+Description:
+		The firmware provides DMI structures as a packed list of
+		data referenced by a SMBIOS table entry point. The SMBIOS
+		entry point contains general information, like SMBIOS
+		version, DMI table size, etc. The structure, content and
+		size of SMBIOS entry point is dependent on SMBIOS version.
+		The format of SMBIOS entry point and DMI structures
+		can be read in SMBIOS specification.
+
+		The dmi/tables provides raw SMBIOS entry point and DMI tables
+		through sysfs as an alternative to utilities reading them
+		from /dev/mem. The raw SMBIOS entry point and DMI table are
+		presented as binary attributes and are accessible via:
+
+		/sys/firmware/dmi/tables/smbios_entry_point
+		/sys/firmware/dmi/tables/DMI
+
+		The complete DMI information can be obtained using these two
+		tables.

MAINTAINERS

···
 M:	Jean Delvare <[e-mail]>
 S:	Maintained
 T:	quilt http://jdelvare.nerim.net/devel/linux/jdelvare-dmi/
+F:	Documentation/ABI/testing/sysfs-firmware-dmi-tables
 F:	drivers/firmware/dmi-id.c
 F:	drivers/firmware/dmi_scan.c
 F:	include/linux/dmi.h

drivers/firmware/dmi-sysfs.c

···
 	.default_attrs = dmi_sysfs_entry_attrs,
 };
 
-static struct kobject *dmi_kobj;
 static struct kset *dmi_kset;
 
 /* Global count of all instances seen.  Only for setup */
···
 
 static int __init dmi_sysfs_init(void)
 {
-	int error = -ENOMEM;
+	int error;
 	int val;
 
-	/* Set up our directory */
-	dmi_kobj = kobject_create_and_add("dmi", firmware_kobj);
-	if (!dmi_kobj)
+	if (!dmi_kobj) {
+		pr_err("dmi-sysfs: dmi entry is absent.\n");
+		error = -ENODATA;
 		goto err;
+	}
 
 	dmi_kset = kset_create_and_add("entries", NULL, dmi_kobj);
-	if (!dmi_kset)
+	if (!dmi_kset) {
+		error = -ENOMEM;
 		goto err;
+	}
 
 	val = 0;
 	error = dmi_walk(dmi_sysfs_register_handle, &val);
···
 err:
 	cleanup_entry_list();
 	kset_unregister(dmi_kset);
-	kobject_put(dmi_kobj);
 	return error;
 }
 
···
 	pr_debug("dmi-sysfs: unloading.\n");
 	cleanup_entry_list();
 	kset_unregister(dmi_kset);
-	kobject_del(dmi_kobj);
-	kobject_put(dmi_kobj);
 }
 
 module_init(dmi_sysfs_init);

drivers/firmware/dmi_scan.c

···
 #include <asm/dmi.h>
 #include <asm/unaligned.h>
 
+struct kobject *dmi_kobj;
+EXPORT_SYMBOL_GPL(dmi_kobj);
+
 /*
  * DMI stands for "Desktop Management Interface".  It is part
  * of and an antecedent to, SMBIOS, which stands for System
···
 static u32 dmi_ver __initdata;
 static u32 dmi_len;
 static u16 dmi_num;
+static u8 smbios_entry_point[32];
+static int smbios_entry_point_size;
+
 /*
  * Catch too early calls to dmi_check_system():
  */
···
 	if (memcmp(buf, "_SM_", 4) == 0 &&
 	    buf[5] < 32 && dmi_checksum(buf, buf[5])) {
 		smbios_ver = get_unaligned_be16(buf + 6);
+		smbios_entry_point_size = buf[5];
+		memcpy(smbios_entry_point, buf, smbios_entry_point_size);
 
 		/* Some BIOS report weird SMBIOS version, fix that up */
 		switch (smbios_ver) {
···
 				pr_info("SMBIOS %d.%d present.\n",
 				       dmi_ver >> 8, dmi_ver & 0xFF);
 			} else {
+				smbios_entry_point_size = 15;
+				memcpy(smbios_entry_point, buf,
+				       smbios_entry_point_size);
 				pr_info("Legacy DMI %d.%d present.\n",
 				       dmi_ver >> 8, dmi_ver & 0xFF);
 			}
···
 		dmi_num = 0;			/* No longer specified */
 		dmi_len = get_unaligned_le32(buf + 12);
 		dmi_base = get_unaligned_le64(buf + 16);
+		smbios_entry_point_size = buf[6];
+		memcpy(smbios_entry_point, buf, smbios_entry_point_size);
 
 		if (dmi_walk_early(dmi_decode) == 0) {
 			pr_info("SMBIOS %d.%d.%d present.\n",
···
  out:
 	dmi_initialized = 1;
 }
+
+static ssize_t raw_table_read(struct file *file, struct kobject *kobj,
+			      struct bin_attribute *attr, char *buf,
+			      loff_t pos, size_t count)
+{
+	memcpy(buf, attr->private + pos, count);
+	return count;
+}
+
+static BIN_ATTR(smbios_entry_point, S_IRUSR, raw_table_read, NULL, 0);
+static BIN_ATTR(DMI, S_IRUSR, raw_table_read, NULL, 0);
+
+static int __init dmi_init(void)
+{
+	struct kobject *tables_kobj;
+	u8 *dmi_table;
+	int ret = -ENOMEM;
+
+	if (!dmi_available) {
+		ret = -ENODATA;
+		goto err;
+	}
+
+	/*
+	 * Set up dmi directory at /sys/firmware/dmi. This entry should stay
+	 * even after farther error, as it can be used by other modules like
+	 * dmi-sysfs.
+	 */
+	dmi_kobj = kobject_create_and_add("dmi", firmware_kobj);
+	if (!dmi_kobj)
+		goto err;
+
+	tables_kobj = kobject_create_and_add("tables", dmi_kobj);
+	if (!tables_kobj)
+		goto err;
+
+	dmi_table = dmi_remap(dmi_base, dmi_len);
+	if (!dmi_table)
+		goto err_tables;
+
+	bin_attr_smbios_entry_point.size = smbios_entry_point_size;
+	bin_attr_smbios_entry_point.private = smbios_entry_point;
+	ret = sysfs_create_bin_file(tables_kobj, &bin_attr_smbios_entry_point);
+	if (ret)
+		goto err_unmap;
+
+	bin_attr_DMI.size = dmi_len;
+	bin_attr_DMI.private = dmi_table;
+	ret = sysfs_create_bin_file(tables_kobj, &bin_attr_DMI);
+	if (!ret)
+		return 0;
+
+	sysfs_remove_bin_file(tables_kobj,
+			      &bin_attr_smbios_entry_point);
+ err_unmap:
+	dmi_unmap(dmi_table);
+ err_tables:
+	kobject_del(tables_kobj);
+	kobject_put(tables_kobj);
+ err:
+	pr_err("dmi: Firmware registration failed.\n");
+
+	return ret;
+}
+subsys_initcall(dmi_init);
 
 /**
  * dmi_set_dump_stack_arch_desc - set arch description for dump_stack()

include/linux/dmi.h

···
 #define __DMI_H__
 
 #include <linux/list.h>
+#include <linux/kobject.h>
 #include <linux/mod_devicetable.h>
 
 /* enum dmi_field is in mod_devicetable.h */
···
 	int devfn;
 };
 
+extern struct kobject *dmi_kobj;
 extern int dmi_check_system(const struct dmi_system_id *list);
 const struct dmi_system_id *dmi_first_match(const struct dmi_system_id *list);
 extern const char * dmi_get_system_info(int field);