mmc: MMC boot partitions support.

Allows device MMC boot partitions to be accessed. MMC partitions are
treated effectively as separate block devices on the same MMC card.
Signed-off-by: Andrei Warkentin <andreiw@motorola.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Chris Ball <cjb@laptop.org>

Documentation/mmc/00-INDEX

@@ -2,3 +2,5 @@
         - this file
 mmc-dev-attrs.txt
         - info on SD and MMC device attributes
+mmc-dev-parts.txt
+        - info on SD and MMC device partitions

Documentation/mmc/mmc-dev-attrs.txt

+SD and MMC Block Device Attributes
+==================================
+
+These attributes are defined for the block devices associated with the
+SD or MMC device.
+
+The following attributes are read/write.
+
+	force_ro		Enforce read-only access even if write protect switch is off.
+
 SD and MMC Device Attributes
 ============================
 

Documentation/mmc/mmc-dev-parts.txt

+SD and MMC Device Partitions
+============================
+
+Device partitions are additional logical block devices present on the
+SD/MMC device.
+
+As of this writing, MMC boot partitions as supported and exposed as
+/dev/mmcblkXboot0 and /dev/mmcblkXboot1, where X is the index of the
+parent /dev/mmcblkX.
+
+MMC Boot Partitions
+===================
+
+Read and write access is provided to the two MMC boot partitions. Due to
+the sensitive nature of the boot partition contents, which often store
+a bootloader or bootloader configuration tables crucial to booting the
+platform, write access is disabled by default to reduce the chance of
+accidental bricking.
+
+To enable write access to /dev/mmcblkXbootY, disable the forced read-only
+access with:
+
+echo 0 > /sys/block/mmcblkXbootY/force_ro
+
+To re-enable read-only access:
+
+echo 1 > /sys/block/mmcblkXbootY/force_ro

drivers/mmc/core/mmc.c

@@ -288,7 +288,10 @@ static int mmc_read_ext_csd(struct mmc_card *card)
 
 	if (card->ext_csd.rev >= 3) {
 		u8 sa_shift = ext_csd[EXT_CSD_S_A_TIMEOUT];
-		card->ext_csd.bootconfig = ext_csd[EXT_CSD_BOOT_CONFIG];
+		card->ext_csd.part_config = ext_csd[EXT_CSD_PART_CONFIG];
+
+		/* EXT_CSD value is in units of 10ms, but we store in ms */
+		card->ext_csd.part_time = 10 * ext_csd[EXT_CSD_PART_SWITCH_TIME];
 
 		/* Sleep / awake timeout in 100ns units */
 		if (sa_shift > 0 && sa_shift <= 0x17)
@@ -302,6 +305,12 @@ static int mmc_read_ext_csd(struct mmc_card *card)
 			ext_csd[EXT_CSD_HC_ERASE_GRP_SIZE] << 10;
 
 		card->ext_csd.rel_sectors = ext_csd[EXT_CSD_REL_WR_SEC_C];
+
+		/*
+		 * There are two boot regions of equal size, defined in
+		 * multiples of 128K.
+		 */
+		card->ext_csd.boot_size = ext_csd[EXT_CSD_BOOT_MULT] << 17;
 	}
 
 	if (card->ext_csd.rev >= 4) {
@@ -576,10 +585,13 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
 	/*
 	 * Ensure eMMC user default partition is enabled
 	 */
-	if (card->ext_csd.bootconfig & 0x7) {
-		card->ext_csd.bootconfig &= ~0x7;
-		mmc_switch(card, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_BOOT_CONFIG,
-			   card->ext_csd.bootconfig, 0);
+	if (card->ext_csd.part_config & EXT_CSD_PART_CONFIG_ACC_MASK) {
+		card->ext_csd.part_config &= ~EXT_CSD_PART_CONFIG_ACC_MASK;
+		err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_PART_CONFIG,
+				 card->ext_csd.part_config,
+				 card->ext_csd.part_time);
+		if (err && err != -EBADMSG)
+			goto free_card;
 	}
 
 	/*

include/linux/mmc/card.h

@@ -48,7 +48,8 @@ struct mmc_ext_csd {
 	u8			sec_feature_support;
 	u8			rel_sectors;
 	u8			rel_param;
-	u8			bootconfig;
+	u8			part_config;
+	unsigned int		part_time;		/* Units: ms */
 	unsigned int		sa_timeout;		/* Units: 100ns */
 	unsigned int		hs_max_dtr;
 	unsigned int		sectors;
@@ -61,6 +62,7 @@ struct mmc_ext_csd {
 	bool			enhanced_area_en;	/* enable bit */
 	unsigned long long	enhanced_area_offset;	/* Units: Byte */
 	unsigned int		enhanced_area_size;	/* Units: KB */
+	unsigned int		boot_size;		/* in bytes */
 };
 
 struct sd_scr {

include/linux/mmc/mmc.h

@@ -257,19 +257,21 @@ struct _mmc_csd {
 #define EXT_CSD_PARTITION_SUPPORT	160	/* RO */
 #define EXT_CSD_WR_REL_PARAM		166	/* RO */
 #define EXT_CSD_ERASE_GROUP_DEF		175	/* R/W */
-#define EXT_CSD_BOOT_CONFIG		179	/* R/W */
+#define EXT_CSD_PART_CONFIG		179	/* R/W */
 #define EXT_CSD_ERASED_MEM_CONT		181	/* RO */
 #define EXT_CSD_BUS_WIDTH		183	/* R/W */
 #define EXT_CSD_HS_TIMING		185	/* R/W */
 #define EXT_CSD_REV			192	/* RO */
 #define EXT_CSD_STRUCTURE		194	/* RO */
 #define EXT_CSD_CARD_TYPE		196	/* RO */
+#define EXT_CSD_PART_SWITCH_TIME        199     /* RO */
 #define EXT_CSD_SEC_CNT			212	/* RO, 4 bytes */
 #define EXT_CSD_S_A_TIMEOUT		217	/* RO */
 #define EXT_CSD_REL_WR_SEC_C		222	/* RO */
 #define EXT_CSD_HC_WP_GRP_SIZE		221	/* RO */
 #define EXT_CSD_ERASE_TIMEOUT_MULT	223	/* RO */
 #define EXT_CSD_HC_ERASE_GRP_SIZE	224	/* RO */
+#define EXT_CSD_BOOT_MULT		226	/* RO */
 #define EXT_CSD_SEC_TRIM_MULT		229	/* RO */
 #define EXT_CSD_SEC_ERASE_MULT		230	/* RO */
 #define EXT_CSD_SEC_FEATURE_SUPPORT	231	/* RO */
@@ -281,6 +283,10 @@ struct _mmc_csd {
 
 #define EXT_CSD_WR_REL_PARAM_EN		(1<<2)
 
+#define EXT_CSD_PART_CONFIG_ACC_MASK	(0x7)
+#define EXT_CSD_PART_CONFIG_ACC_BOOT0	(0x1)
+#define EXT_CSD_PART_CONFIG_ACC_BOOT1	(0x2)
+
 #define EXT_CSD_CMD_SET_NORMAL		(1<<0)
 #define EXT_CSD_CMD_SET_SECURE		(1<<1)
 #define EXT_CSD_CMD_SET_CPSECURE	(1<<2)