[PATCH 3/5] mmc: core: changes frequency to hs_max_dtr when selecting hs400es

From: Shawn Lin
Date: Tue Sep 20 2016 - 21:43:41 EST

Per JESD84-B51 P69, Host need to change frequency to <=52MHz after
setting HS_TIMING to 0x1, and host may changes frequency to <= 200MHz
after setting HS_TIMING to 0x3. It seems there is no difference if
we don't change frequency to <= 52MHz as f_init is already less than
52MHz. But actually it does make difference. When doing compatibility
test we see failures for some eMMC devices without changing the
frequency to hs_max_dtr. And let's read the spec again, we could see
that "Host may changes frequency to 200MHz" implies that it's not
mandatory. But the "Host need to change frequency to <= 52MHz" implies
that we should do this.

Reported-by: Xiao Yao <xiaoyao@xxxxxxxxxxxxxx>
Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>

drivers/mmc/core/mmc.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 3163bb9..989d37e 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1282,6 +1282,8 @@ static int mmc_select_hs400es(struct mmc_card *card)
if (err)
goto out_err;

+ mmc_set_clock(host, card->ext_csd.hs_max_dtr);
err = mmc_switch_status(card);
if (err)
goto out_err;