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

From: Shawn Lin
Date: Thu Sep 22 2016 - 19:34:30 EST

On 2016/9/22 18:21, Ulf Hansson wrote:
On 22 September 2016 at 12:06, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
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.

Okay, I see what you mean now!

In other words:
The card expects the clock rate to increase from the current used
f_init (which is <= 400KHz), but still being <= 52MHz, when you have
set HS_TIMING to 0x1.

Okay, we can do that change! Could you try to improve the change log a
little bit or you want me to help?

yep, I could change the commit msg a bit and fix another
copy-paste error, then respin v2.
BTW, I noticed you have applied one of these 5 patches, so
I will remove that one for V2.

Thanks, Ulf.

Kind regards

Best Regards
Shawn Lin