Re: [PATCH 2/2] mmc: core: fall back host->f_init if failing to init mmc card after resume

[Shawn Lin]

å 2016/7/19 18:31, Ulf Hansson åé:
> On 19 July 2016 at 10:58, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
> > We observed the failure of initializing card after resume
> > accidentally. It's hard to reproduce but we did get report from
> > the suspend/resume test of our RK3399 mp test farm . Unfortunately,
> > we still fail to figure out what was going wrong at that time.
> > Also we can't achieve it by retrying the host->f_init without falling
> > back it. But this patch will solve the problem as we could add some log
> > there and see that we resume the mmc card successfully after falling
> > back the host->f_init. There is no obvious side effect found, so it seems
> > this patch will improve the stability.
>
> What f_init did the original rescan work find out being successful?

The original f_init was 400k when booting up the system.

> Did you then verify that it was *another* frequency that made the
> initialization to work in the resume?

yes, I added some log and saw 100k made the initialization to work in
the resume finally with the patch applied.

Also I mentioned in the commit msg that if I just retried 400K, it
cannot made the initialization successful.

> > [   93.405085] mmc1: unexpected status 0x800900 after switch
> > [   93.408474] mmc1: switch to bus width 1 failed
> > [   93.408482] mmc1: mmc_select_hs200 failed, error -110
> > [   93.408492] mmc1: error -110 during resume (card was removed?)
> > [   93.408705] PM: resume of devices complete after 213.453 msecs
> >
> > Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
> > ---
> >
> >  drivers/mmc/core/mmc.c | 22 ++++++++++++++++++++--
> >  1 file changed, 20 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> > index 403b97b..bef40c8 100644
> > --- a/drivers/mmc/core/mmc.c
> > +++ b/drivers/mmc/core/mmc.c
> > @@ -1945,6 +1945,7 @@ static int mmc_suspend(struct mmc_host *host)
> >  static int _mmc_resume(struct mmc_host *host)
> >  {
> >         int err = 0;
> > +       int i;
> >
> >         BUG_ON(!host);
> >         BUG_ON(!host->card);
> > @@ -1954,8 +1955,25 @@ static int _mmc_resume(struct mmc_host *host)
> >         if (!mmc_card_suspended(host->card))
> >                 goto out;
> >
> > -       mmc_power_up(host, host->card->ocr);
> > -       err = mmc_init_card(host, host->card->ocr, host->card);
> > +       /*
> > +        * Let's try to fallback the host->f_init
> > +        * if failing to init card after resume.
> > +        */
> > +
> > +       for (i = 0; i < ARRAY_SIZE(freqs); i++) {
> > +               if (host->f_init < freqs[i])
> > +                       continue;
> > +               else
> > +                       host->f_init = freqs[i];
>
> This loop is wrong, as you don't consider that host->f_min may not
> exactly match the frequencies in the freqs array.

Ah, seems I should use 'max(freqs[i], host->f_min)'.. :)

> > +
> > +               mmc_power_up(host, host->card->ocr);
> > +               err = mmc_init_card(host, host->card->ocr, host->card);
> > +               if (!err)
> > +                       break;
> > +
> > +               mmc_power_off(host);
>
> The mmc core expects the host/card to be powered up after a resume, as
> it may send commands to it without first invoking mmc_power_up().
> Even if those commands may fail (or timeout), at least those doesn't
> hang which may be the case if the host/card isn't powered up first.

I got it, thanks.

> So, you must *not* leave the host/card in "mmc_power_off()" state in
> _mmc_resume().
>
> [...]
>
> Kind regards
> Uffe


--
Best Regards
Shawn Lin