mmc: block: Support alternative_gpt_sector() operation

Support generic alternative_gpt_sector() block device operation.
It calculates location of GPT entry for eMMC of NVIDIA Tegra Android
devices. Add new MMC_CAP2_ALT_GPT_TEGRA flag that enables scanning of
alternative GPT sector and add raw_boot_mult field to mmc_ext_csd
which allows to get size of the boot partitions that is needed for
the calculation.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210820004536.15791-4-digetx@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/mmc/core/block.c

@@ -831,6 +831,26 @@ static int mmc_blk_compat_ioctl(struct block_device *bdev, fmode_t mode,
 }
 #endif
 
+static int mmc_blk_alternative_gpt_sector(struct gendisk *disk,
+					  sector_t *sector)
+{
+	struct mmc_blk_data *md;
+	int ret;
+
+	md = mmc_blk_get(disk);
+	if (!md)
+		return -EINVAL;
+
+	if (md->queue.card)
+		ret = mmc_card_alternative_gpt_sector(md->queue.card, sector);
+	else
+		ret = -ENODEV;
+
+	mmc_blk_put(md);
+
+	return ret;
+}
+
 static const struct block_device_operations mmc_bdops = {
 	.open			= mmc_blk_open,
 	.release		= mmc_blk_release,
@@ -840,6 +860,7 @@ static const struct block_device_operations mmc_bdops = {
 #ifdef CONFIG_COMPAT
 	.compat_ioctl		= mmc_blk_compat_ioctl,
 #endif
+	.alternative_gpt_sector	= mmc_blk_alternative_gpt_sector,
 };
 
 static int mmc_blk_part_switch_pre(struct mmc_card *card,

drivers/mmc/core/core.c

@@ -2149,6 +2149,41 @@ int mmc_detect_card_removed(struct mmc_host *host)
 }
 EXPORT_SYMBOL(mmc_detect_card_removed);
 
+int mmc_card_alternative_gpt_sector(struct mmc_card *card, sector_t *gpt_sector)
+{
+	unsigned int boot_sectors_num;
+
+	if ((!(card->host->caps2 & MMC_CAP2_ALT_GPT_TEGRA)))
+		return -EOPNOTSUPP;
+
+	/* filter out unrelated cards */
+	if (card->ext_csd.rev < 3 ||
+	    !mmc_card_mmc(card) ||
+	    !mmc_card_is_blockaddr(card) ||
+	     mmc_card_is_removable(card->host))
+		return -ENOENT;
+
+	/*
+	 * eMMC storage has two special boot partitions in addition to the
+	 * main one.  NVIDIA's bootloader linearizes eMMC boot0->boot1->main
+	 * accesses, this means that the partition table addresses are shifted
+	 * by the size of boot partitions.  In accordance with the eMMC
+	 * specification, the boot partition size is calculated as follows:
+	 *
+	 *	boot partition size = 128K byte x BOOT_SIZE_MULT
+	 *
+	 * Calculate number of sectors occupied by the both boot partitions.
+	 */
+	boot_sectors_num = card->ext_csd.raw_boot_mult * SZ_128K /
+			   SZ_512 * MMC_NUM_BOOT_PARTITION;
+
+	/* Defined by NVIDIA and used by Android devices. */
+	*gpt_sector = card->ext_csd.sectors - boot_sectors_num - 1;
+
+	return 0;
+}
+EXPORT_SYMBOL(mmc_card_alternative_gpt_sector);
+
 void mmc_rescan(struct work_struct *work)
 {
 	struct mmc_host *host =

drivers/mmc/core/core.h

@@ -119,6 +119,8 @@ void mmc_release_host(struct mmc_host *host);
 void mmc_get_card(struct mmc_card *card, struct mmc_ctx *ctx);
 void mmc_put_card(struct mmc_card *card, struct mmc_ctx *ctx);
 
+int mmc_card_alternative_gpt_sector(struct mmc_card *card, sector_t *sector);
+
 /**
  *	mmc_claim_host - exclusively claim a host
  *	@host: mmc host to claim

drivers/mmc/core/mmc.c

@@ -418,6 +418,8 @@ static int mmc_decode_ext_csd(struct mmc_card *card, u8 *ext_csd)
 		ext_csd[EXT_CSD_ERASE_TIMEOUT_MULT];
 	card->ext_csd.raw_hc_erase_grp_size =
 		ext_csd[EXT_CSD_HC_ERASE_GRP_SIZE];
+	card->ext_csd.raw_boot_mult =
+		ext_csd[EXT_CSD_BOOT_MULT];
 	if (card->ext_csd.rev >= 3) {
 		u8 sa_shift = ext_csd[EXT_CSD_S_A_TIMEOUT];
 		card->ext_csd.part_config = ext_csd[EXT_CSD_PART_CONFIG];

include/linux/mmc/card.h

@@ -109,6 +109,7 @@ struct mmc_ext_csd {
 	u8			raw_hc_erase_gap_size;	/* 221 */
 	u8			raw_erase_timeout_mult;	/* 223 */
 	u8			raw_hc_erase_grp_size;	/* 224 */
+	u8			raw_boot_mult;		/* 226 */
 	u8			raw_sec_trim_mult;	/* 229 */
 	u8			raw_sec_erase_mult;	/* 230 */
 	u8			raw_sec_feature_support;/* 231 */

include/linux/mmc/host.h

@@ -398,6 +398,7 @@ struct mmc_host {
 #else
 #define MMC_CAP2_CRYPTO		0
 #endif
+#define MMC_CAP2_ALT_GPT_TEGRA	(1 << 28)	/* Host with eMMC that has GPT entry at a non-standard location */
 
 	int			fixed_drv_type;	/* fixed driver type for non-removable media */