[PATCH v2 2/3] mmc: erase: Use TRIM erase when available

[Loic Poulain]

The default erase command applies on erase group unit, and
simply round down to erase group size. When the start block
is not aligned to erase group size (e.g. erasing partition)
it causes unwanted erasing of the previous blocks, part of
the same erase group (e.g. owned by other logical partition,
or by the partition table itself).

To prevent this issue, a simple solution is to use TRIM as
argument of the Erase command, which is usually supported
with eMMC > 4.0, and allow to apply erase operation to write
blocks instead of erase group

Signed-off-by: Loic Poulain <loic.poulain at linaro.org>
---
v2: Add mmc unit test change to the series

 drivers/mmc/mmc_write.c | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/drivers/mmc/mmc_write.c b/drivers/mmc/mmc_write.c
index 5b7aeeb012..a6f93380dd 100644
--- a/drivers/mmc/mmc_write.c
+++ b/drivers/mmc/mmc_write.c
@@ -15,7 +15,7 @@
 #include <linux/math64.h>
 #include "mmc_private.h"
 
-static ulong mmc_erase_t(struct mmc *mmc, ulong start, lbaint_t blkcnt)
+static ulong mmc_erase_t(struct mmc *mmc, ulong start, lbaint_t blkcnt, u32 args)
 {
 	struct mmc_cmd cmd;
 	ulong end;
@@ -52,7 +52,7 @@ static ulong mmc_erase_t(struct mmc *mmc, ulong start, lbaint_t blkcnt)
 		goto err_out;
 
 	cmd.cmdidx = MMC_CMD_ERASE;
-	cmd.cmdarg = MMC_ERASE_ARG;
+	cmd.cmdarg = args ? args : MMC_ERASE_ARG;
 	cmd.resp_type = MMC_RSP_R1b;
 
 	err = mmc_send_cmd(mmc, &cmd, NULL);
@@ -77,7 +77,7 @@ ulong mmc_berase(struct blk_desc *block_dev, lbaint_t start, lbaint_t blkcnt)
 #endif
 	int dev_num = block_dev->devnum;
 	int err = 0;
-	u32 start_rem, blkcnt_rem;
+	u32 start_rem, blkcnt_rem, erase_args = 0;
 	struct mmc *mmc = find_mmc_device(dev_num);
 	lbaint_t blk = 0, blk_r = 0;
 	int timeout_ms = 1000;
@@ -97,13 +97,25 @@ ulong mmc_berase(struct blk_desc *block_dev, lbaint_t start, lbaint_t blkcnt)
 	 */
 	err = div_u64_rem(start, mmc->erase_grp_size, &start_rem);
 	err = div_u64_rem(blkcnt, mmc->erase_grp_size, &blkcnt_rem);
-	if (start_rem || blkcnt_rem)
-		printf("\n\nCaution! Your devices Erase group is 0x%x\n"
-		       "The erase range would be change to "
-		       "0x" LBAF "~0x" LBAF "\n\n",
-		       mmc->erase_grp_size, start & ~(mmc->erase_grp_size - 1),
-		       ((start + blkcnt + mmc->erase_grp_size - 1)
-		       & ~(mmc->erase_grp_size - 1)) - 1);
+	if (start_rem || blkcnt_rem) {
+		if (mmc->can_trim) {
+			/* Trim function applies the erase operation to write
+			 * blocks instead of erase groups.
+			 */
+			erase_args = MMC_TRIM_ARG;
+		} else {
+			/* The card ignores all LSB's below the erase group
+			 * size, rounding down the addess to a erase group
+			 * boundary.
+			 */
+			printf("\n\nCaution! Your devices Erase group is 0x%x\n"
+			       "The erase range would be change to "
+			       "0x" LBAF "~0x" LBAF "\n\n",
+			       mmc->erase_grp_size, start & ~(mmc->erase_grp_size - 1),
+			       ((start + blkcnt + mmc->erase_grp_size - 1)
+			       & ~(mmc->erase_grp_size - 1)) - 1);
+		}
+	}
 
 	while (blk < blkcnt) {
 		if (IS_SD(mmc) && mmc->ssr.au) {
@@ -113,7 +125,7 @@ ulong mmc_berase(struct blk_desc *block_dev, lbaint_t start, lbaint_t blkcnt)
 			blk_r = ((blkcnt - blk) > mmc->erase_grp_size) ?
 				mmc->erase_grp_size : (blkcnt - blk);
 		}
-		err = mmc_erase_t(mmc, start + blk, blk_r);
+		err = mmc_erase_t(mmc, start + blk, blk_r, erase_args);
 		if (err)
 			break;
 
-- 
2.34.1