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

From: Ulf Hansson
Date: Thu Sep 22 2016 - 06:21:24 EST

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?

Kind regards