mmc: core: new discard feature support at eMMC v4.5

MMC v4.5 supports the DISCARD feature (CMD38).  It's different from
trim and there's no check bit.  Currently it's only supported at v4.5.
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/card/block.c

@@ -756,7 +756,9 @@ static int mmc_blk_issue_discard_rq(struct mmc_queue *mq, struct request *req)
 	from = blk_rq_pos(req);
 	nr = blk_rq_sectors(req);
 
-	if (mmc_can_trim(card))
+	if (mmc_can_discard(card))
+		arg = MMC_DISCARD_ARG;
+	else if (mmc_can_trim(card))
 		arg = MMC_TRIM_ARG;
 	else
 		arg = MMC_ERASE_ARG;

drivers/mmc/core/core.c

@@ -1709,10 +1709,24 @@ int mmc_can_trim(struct mmc_card *card)
 {
 	if (card->ext_csd.sec_feature_support & EXT_CSD_SEC_GB_CL_EN)
 		return 1;
+	if (mmc_can_discard(card))
+		return 1;
 	return 0;
 }
 EXPORT_SYMBOL(mmc_can_trim);
 
+int mmc_can_discard(struct mmc_card *card)
+{
+	/*
+	 * As there's no way to detect the discard support bit at v4.5
+	 * use the s/w feature support filed.
+	 */
+	if (card->ext_csd.feature_support & MMC_DISCARD_FEATURE)
+		return 1;
+	return 0;
+}
+EXPORT_SYMBOL(mmc_can_discard);
+
 int mmc_can_sanitize(struct mmc_card *card)
 {
 	if (card->ext_csd.sec_feature_support & EXT_CSD_SEC_SANITIZE)

drivers/mmc/core/mmc.c

@@ -452,6 +452,10 @@ static int mmc_read_ext_csd(struct mmc_card *card, u8 *ext_csd)
 		card->ext_csd.rst_n_function = ext_csd[EXT_CSD_RST_N_FUNCTION];
 	}
 
+	/* eMMC v4.5 or later */
+	if (card->ext_csd.rev >= 6)
+		card->ext_csd.feature_support |= MMC_DISCARD_FEATURE;
+
 	card->ext_csd.raw_erased_mem_count = ext_csd[EXT_CSD_ERASED_MEM_CONT];
 	if (ext_csd[EXT_CSD_ERASED_MEM_CONT])
 		card->erased_byte = 0xFF;

include/linux/mmc/card.h

@@ -80,6 +80,9 @@ struct mmc_ext_csd {
 	u8			raw_sec_feature_support;/* 231 */
 	u8			raw_trim_mult;		/* 232 */
 	u8			raw_sectors[4];		/* 212 - 4 bytes */
+
+	unsigned int            feature_support;
+#define MMC_DISCARD_FEATURE	BIT(0)                  /* CMD38 feature */
 };
 
 struct sd_scr {

include/linux/mmc/core.h

@@ -146,6 +146,7 @@ extern int mmc_switch(struct mmc_card *, u8, u8, u8, unsigned int);
 #define MMC_ERASE_ARG		0x00000000
 #define MMC_SECURE_ERASE_ARG	0x80000000
 #define MMC_TRIM_ARG		0x00000001
+#define MMC_DISCARD_ARG		0x00000003
 #define MMC_SECURE_TRIM1_ARG	0x80000001
 #define MMC_SECURE_TRIM2_ARG	0x80008000
 
@@ -156,6 +157,7 @@ extern int mmc_erase(struct mmc_card *card, unsigned int from, unsigned int nr,
 		     unsigned int arg);
 extern int mmc_can_erase(struct mmc_card *card);
 extern int mmc_can_trim(struct mmc_card *card);
+extern int mmc_can_discard(struct mmc_card *card);
 extern int mmc_can_sanitize(struct mmc_card *card);
 extern int mmc_can_secure_erase_trim(struct mmc_card *card);
 extern int mmc_erase_group_aligned(struct mmc_card *card, unsigned int from,