[4.2.y-ckt stable] Patch "mmc: mmc: Improve reliability of mmc_select_hs200()" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    mmc: mmc: Improve reliability of mmc_select_hs200()

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 57f65c4ee11d1577178809d2cd0ff33c5ad27a62 Mon Sep 17 00:00:00 2001
From: Adrian Hunter <adrian.hunter at intel.com>
Date: Wed, 28 Oct 2015 14:25:40 +0200
Subject: mmc: mmc: Improve reliability of mmc_select_hs200()

commit 1815e61b1a7efe81017a883e817292daf7d2f922 upstream.

Currently mmc_select_hs200() uses __mmc_switch() which checks the
success of the switch to HS200 mode using CMD13 (SEND_STATUS).
The problem is that it does that using the timing settings of legacy
mode.  That is prone to error, not least because the timing parameters
for legacy mode are tighter than the timing parameters for HS200 mode.

In the case when CMD13 polling is used (i.e. not MMC_CAP_WAIT_WHILE_BUSY)
with the switch command, it must be assumed that using different modes on
the card and host must work.

However in the case when CMD13 polling is not used
(i.e. MMC_CAP_WAIT_WHILE_BUSY) mmc_select_hs200() can be made more
reliable by setting the host to the correct timing before sending CMD13.

This patch does that.

A complication is that the caller, mmc_select_timing(), will ignore a
switch error (indicated by -EBADMSG), assume the old mode is valid
and continue, so the old timing must be restored in that case.

Signed-off-by: Adrian Hunter <adrian.hunter at intel.com>
Tested-by: Alim Akhtar <alim.akhtar at samsung.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 | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index f6cd995..3d4e7f7 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1219,6 +1219,8 @@ static void mmc_select_driver_type(struct mmc_card *card)
 static int mmc_select_hs200(struct mmc_card *card)
 {
 	struct mmc_host *host = card->host;
+	bool send_status = true;
+	unsigned int old_timing;
 	int err = -EINVAL;
 	u8 val;

@@ -1234,6 +1236,9 @@ static int mmc_select_hs200(struct mmc_card *card)

 	mmc_select_driver_type(card);

+	if (host->caps & MMC_CAP_WAIT_WHILE_BUSY)
+		send_status = false;
+
 	/*
 	 * Set the bus width(4 or 8) with host's support and
 	 * switch to HS200 mode if bus width is set successfully.
@@ -1245,11 +1250,25 @@ static int mmc_select_hs200(struct mmc_card *card)
 		err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
 				   EXT_CSD_HS_TIMING, val,
 				   card->ext_csd.generic_cmd6_time,
-				   true, true, true);
-		if (!err)
-			mmc_set_timing(host, MMC_TIMING_MMC_HS200);
+				   true, send_status, true);
+		if (err)
+			goto err;
+		old_timing = host->ios.timing;
+		mmc_set_timing(host, MMC_TIMING_MMC_HS200);
+		if (!send_status) {
+			err = mmc_switch_status(card);
+			/*
+			 * mmc_select_timing() assumes timing has not changed if
+			 * it is a switch error.
+			 */
+			if (err == -EBADMSG)
+				mmc_set_timing(host, old_timing);
+		}
 	}
 err:
+	if (err)
+		pr_err("%s: %s failed, error %d\n", mmc_hostname(card->host),
+		       __func__, err);
 	return err;
 }

--
1.9.1