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

[Ulf Hansson]

On 19 July 2016 at 10:58, Shawn Lin <shawn.lin at rock-chips.com> 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?

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

>
> [   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 at rock-chips.com>
> ---
>
>  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.

> +
> +               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.

So, you must *not* leave the host/card in "mmc_power_off()" state in
_mmc_resume().

[...]

Kind regards
Uffe