Re: [PATCH v1] mmc: mmc: Fix HS setting in mmc_hs400_to_hs200()

[Chaotian Jing]

On Wed, 2019-02-13 at 13:08 +0100, Ulf Hansson wrote:
> On Wed, 13 Feb 2019 at 10:07, Chaotian Jing <chaotian.jing@xxxxxxxxxxxx> wrote:
> >
> > mmc_hs400_to_hs200() begins with the card and host in HS400 mode.
> > Therefore, any commands sent to the card should use HS400 timing.
> > reduce clock frequency to 50Mhz but without host timming change
> > may cause CMD6 response CRC error. because host still running at
> > hs400 mode, and it's hard to find a suitable setting for all eMMC
> > cards when clock frequency reduced to 50Mhz but card & host still
> > in hs400 mode.
> > this patch refers to mmc_select_hs400(), make the reduce clock frequency
> > after card timing change.
> >
> > Signed-off-by: Chaotian Jing <chaotian.jing@xxxxxxxxxxxx>
> > Fixes: ef3d232245ab ("mmc: mmc: Relax checking for switch errors after HS200 switch")
> > ---
> >  drivers/mmc/core/mmc.c | 29 +++++++++++++++++++++++------
> >  1 file changed, 23 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> > index 09c688f..00adc2d 100644
> > --- a/drivers/mmc/core/mmc.c
> > +++ b/drivers/mmc/core/mmc.c
> > @@ -1239,20 +1239,37 @@ int mmc_hs400_to_hs200(struct mmc_card *card)
> >         int err;
> >         u8 val;
> >
> > -       /* Reduce frequency to HS */
> > -       max_dtr = card->ext_csd.hs_max_dtr;
> > -       mmc_set_clock(host, max_dtr);
> > -
> >         /* Switch HS400 to HS DDR */
> >         val = EXT_CSD_TIMING_HS;
> >         err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_HS_TIMING,
> >                            val, card->ext_csd.generic_cmd6_time, 0,
> >                            true, false, true);
> > -       if (err)
> > -               goto out_err;
> > +       /*
> > +        * as we are on the way to do re-tune, so if the CMD6 got response CRC
> > +        * error, do not treat it as error.
> > +        */
> > +       if (err) {
> > +               if (err == -EILSEQ) {
> > +                       /*
> > +                        * card will busy after sending out response and host
> > +                        * driver may not wait busy de-assert when get
> > +                        * response CRC error. so just wait enough time to
> > +                        * ensure card leave busy state.
> > +                        */
> > +                       mmc_delay(card->ext_csd.generic_cmd6_time);
> > +                       pr_debug("%s: %s switch to HS got CRC error\n",
> > +                                mmc_hostname(host), __func__);
> > +               } else {
> > +                       goto out_err;
> > +               }
> > +       }
> >
> >         mmc_set_timing(host, MMC_TIMING_MMC_DDR52);
> >
> > +       /* Reduce frequency to HS */
> > +       max_dtr = card->ext_csd.hs_max_dtr;
> > +       mmc_set_clock(host, max_dtr);
> > +
> 
> What Adrian suggested was to not to move this part, but instead, only
> allow CRC errors from the CMD6 as above.
> 
> I guess it didn't work for you?
> 
It should work for me. another issue is CMD6 will be sent 3 times at max
 err = mmc_wait_for_cmd(host, &cmd, MMC_CMD_RETRIES);

if the first CMD6 got response CRC error, then Host driver must wait
busy signal de-assert before send the next CMD6.

So that it really make sense to issue CMD6(R1B) for 3 times ? if host
driver did not handle the first CMD6 response CRC error and send second
CMD6 directly, then this CMD6 will get timeout due to card still in busy
state.
> >         err = mmc_switch_status(card);
> >         if (err)
> >                 goto out_err;
> > --
> > 1.8.1.1.dirty
> >
> 
> Kind regards
> Uffe