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

From: Shawn Lin
Date: Thu Sep 22 2016 - 06:07:08 EST

Hi ulf,

å 2016/9/22 17:38, Ulf Hansson åé:
On 21 September 2016 at 03:43, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
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.

I don't get this. Are you saying that f_init > 52 MHz? That should not
be impossible, right!?

nope, I was saying that the spec implies we to set clock after
setting HS_TIMING to 0x1 when doing hs400es selection.

I thought there is no difference because the spec says "Host need to
change frequency to <= 52MHz", and the f_init(<=400k) is <= 52MHz,
right? So I didn't set clock to hs_max_dtr. But I think I misunderstood
the spec, so this patch will fix this.

So either the core has changed the clock rate by mistake at some other
execution path, or the host driver didn't set the correct clock rate
the first time when invoked via mmc_power_up()?

Kind regards

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;

Best Regards
Shawn Lin