[PATCH v1] mmc: mmc: Fix HS setting in mmc_hs400_to_hs200()

[Chaotian Jing]

mmc_hs400_to_hs200() begins with the card and host in HS400 mode.
Therefore, any commands sent to the card should use HS400 timing.
reduce clock frequency to 50Mhz but without host timming change
may cause CMD6 response CRC error. because host still running at
hs400 mode, and it's hard to find a suitable setting for all eMMC
cards when clock frequency reduced to 50Mhz but card & host still
in hs400 mode.
this patch refers to mmc_select_hs400(), make the reduce clock frequency
after card timing change.

Signed-off-by: Chaotian Jing <chaotian.jing@xxxxxxxxxxxx>
Fixes: ef3d232245ab ("mmc: mmc: Relax checking for switch errors after HS200 switch")
---
 drivers/mmc/core/mmc.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 09c688f..00adc2d 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1239,20 +1239,37 @@ int mmc_hs400_to_hs200(struct mmc_card *card)
 	int err;
 	u8 val;
 
-	/* Reduce frequency to HS */
-	max_dtr = card->ext_csd.hs_max_dtr;
-	mmc_set_clock(host, max_dtr);
-
 	/* Switch HS400 to HS DDR */
 	val = EXT_CSD_TIMING_HS;
 	err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_HS_TIMING,
 			   val, card->ext_csd.generic_cmd6_time, 0,
 			   true, false, true);
-	if (err)
-		goto out_err;
+	/*
+	 * as we are on the way to do re-tune, so if the CMD6 got response CRC
+	 * error, do not treat it as error.
+	 */
+	if (err) {
+		if (err == -EILSEQ) {
+			/*
+			 * card will busy after sending out response and host
+			 * driver may not wait busy de-assert when get
+			 * response CRC error. so just wait enough time to
+			 * ensure card leave busy state.
+			 */
+			mmc_delay(card->ext_csd.generic_cmd6_time);
+			pr_debug("%s: %s switch to HS got CRC error\n",
+				 mmc_hostname(host), __func__);
+		} else {
+			goto out_err;
+		}
+	}
 
 	mmc_set_timing(host, MMC_TIMING_MMC_DDR52);
 
+	/* Reduce frequency to HS */
+	max_dtr = card->ext_csd.hs_max_dtr;
+	mmc_set_clock(host, max_dtr);
+
 	err = mmc_switch_status(card);
 	if (err)
 		goto out_err;
-- 
1.8.1.1.dirty