[PATCH 3.19.y-ckt 68/99] mmc: mmc: Fix partition switch timeout for some eMMCs

Kamal Mostafa kamal at canonical.com
Thu Jul 7 18:38:07 UTC 2016

3.19.8-ckt23 -stable review patch.  If anyone has any objections, please let me know.


From: Adrian Hunter <adrian.hunter at intel.com>

commit 1c447116d017a98c90f8f71c8c5a611e0aa42178 upstream.

Some eMMCs set the partition switch timeout too low.

Now typically eMMCs are considered a critical component (e.g. because
they store the root file system) and consequently are expected to be
reliable.  Thus we can neglect the use case where eMMCs can't switch
reliably and we might want a lower timeout to facilitate speedy

Although we could employ a quirk for the cards that are affected (if
we could identify them all), as described above, there is little
benefit to having a low timeout, so instead simply set a minimum

The minimum is set to 300ms somewhat arbitrarily - the examples that
have been seen had a timeout of 10ms but were sometimes taking 60-70ms.

Signed-off-by: Adrian Hunter <adrian.hunter at intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson at linaro.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 drivers/mmc/core/mmc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 7466ce0..acba480 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -329,6 +329,9 @@ static void mmc_manage_gp_partitions(struct mmc_card *card, u8 *ext_csd)
+/* Minimum partition switch timeout in milliseconds */
  * Decode extended CSD.
@@ -386,6 +389,10 @@ static int mmc_decode_ext_csd(struct mmc_card *card, u8 *ext_csd)
 		/* 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];
+		/* Some eMMC set the value too low so set a minimum */
+		if (card->ext_csd.part_time &&
+		    card->ext_csd.part_time < MMC_MIN_PART_SWITCH_TIME)
+			card->ext_csd.part_time = MMC_MIN_PART_SWITCH_TIME;
 		/* Sleep / awake timeout in 100ns units */
 		if (sa_shift > 0 && sa_shift <= 0x17)

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