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

[Shawn Lin]

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
> Uffe
>
> > 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;
> > --
> > 2.3.7


--
Best Regards
Shawn Lin