Re: [RFC PATCH] mmc: core: HS DDR switch, don't change timing before checking status

[Ludovic Desroches <ludovic.desroches@microchip.com>]

On Fri, Mar 17, 2017 at 04:14:18PM +0100, Ulf Hansson wrote:
> On 10 March 2017 at 15:21, Ludovic Desroches
> <ludovic.desroches@atmel.com> wrote:
> > From: Ludovic Desroches <ludovic.desroches@microchip.com>
> >
> > The commit e173f8911f09 mmc: core: Update CMD13 polling policy when
> > switch to HS DDR mode in addition to fix the management of CRC error,
> > changes the place where the DDR52 timing is set.
> >
> > Before this commit, the sequence was:
> > - set width to 8 with MMC_HS timing
> > - send the switch command
> > - check the status
> > - set width to 8 with MMC_DDR52 timing
> > - send the switch command
> > - check the status
> > Now:
> > - set width to 8 with MMC_HS timing
> > - send the switch command
> > - set width to 8 with MMC_DDR52 timing
> > - check the status
> >
> > It may lead to get an error when checking the status with some devices.
> >
> > Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
> > ---
> >  drivers/mmc/core/mmc.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> > index 0fccca0..b837148 100644
> > --- a/drivers/mmc/core/mmc.c
> > +++ b/drivers/mmc/core/mmc.c
> > @@ -1062,7 +1062,7 @@ static int mmc_select_hs_ddr(struct mmc_card *card)
> >                            EXT_CSD_BUS_WIDTH,
> >                            ext_csd_bits,
> >                            card->ext_csd.generic_cmd6_time,
> > -                          MMC_TIMING_MMC_DDR52,
> > +                          0,
> >                            true, true, true);
> >         if (err) {
> >                 pr_err("%s: switch to bus width %d ddr failed\n",
> > @@ -1106,6 +1106,9 @@ static int mmc_select_hs_ddr(struct mmc_card *card)
> >         if (err)
> >                 err = __mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_330);
> >
> > +       if (!err)
> > +               mmc_set_timing(host, MMC_TIMING_MMC_DDR52);
> > +
> >         return err;
> >  }
> >
> > --
> > 2.9.0
> >
> 
> We had other reports for similar problems. The following change fix
> those issues, have you tried this out?
> 
> [PATCH] mmc: core: Restore parts of the polling policy when switch to HS/HS DDR
> https://patchwork.kernel.org/patch/9515239/

I did the test with next and the behavior is the same.

mmc0: Invalid UHS-I mode selected                          
mmc0: switch to bus width 8 ddr failed                  
mmc0: error -110 whilst initialising MMC card 

It seems the root cause is to perform mmc_set_timing before mmc_switch_status.

Regards

Ludovic