Re: [RFC PATCH V3 02/21] mmc: core: UHS-II support, modify power-up sequence

[Ben Chuang]

Hi Ulf,

On Fri, Jul 17, 2020 at 7:26 PM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> On Fri, 10 Jul 2020 at 13:07, Ben Chuang <benchuanggli@xxxxxxxxx> wrote:
> >
> > From: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
> >
> > According to Fig. 3-35 in "SD Host Controller Simplified Spec. Ver4.20":
> > - Prepare vdd1, vdd2 and ios.timing for using after/in step (2)
> > - chip_select is not used in UHS-II, used to return to the legacy flow
>
> Thanks for pointing to the spec, but please explain why/what/how for
> the change - as this helps me to review.
>
> I am going to stop commenting on each patch's commit message, beyond
> this patch - as it seems the same comment applies to more patches.
>
> >
> > Signed-off-by: Ben Chuang <ben.chuang@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
> > ---
> >  drivers/mmc/core/core.c      | 62 ++++++++++++++++++++++++------------
> >  drivers/mmc/core/regulator.c | 14 ++++++++
> >  2 files changed, 56 insertions(+), 20 deletions(-)
> >
> > diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> > index 8d2b808e9b58..85c83c82ad0c 100644
> > --- a/drivers/mmc/core/core.c
> > +++ b/drivers/mmc/core/core.c
> > @@ -1315,33 +1315,51 @@ void mmc_power_up(struct mmc_host *host, u32 ocr)
> >         if (host->ios.power_mode == MMC_POWER_ON)
> >                 return;
> >
> > -       mmc_pwrseq_pre_power_on(host);
> > +       if (host->flags & MMC_UHS2_SUPPORT) {
> > +               /* TODO: handle 'ocr' parameter */
> > +               host->ios.vdd = fls(host->ocr_avail) - 1;
> > +               host->ios.vdd2 = fls(host->ocr_avail_uhs2) - 1;
> > +               if (mmc_host_is_spi(host))
> > +                       host->ios.chip_select = MMC_CS_HIGH;
> > +               else
> > +                       host->ios.chip_select = MMC_CS_DONTCARE;
> > +               host->ios.timing = MMC_TIMING_UHS2;
>
> If I understand correctly, the intent is to always try to initialize
> the UHS-II interface/phy if that is supported. That doesn't seem
> correct to me. What about if the SD card doesn't support UHS-II, then
> we should use the legacy SD interface instead right?

Please always try UHS-II I/F first, then if UHS-II I/F fails, then
switch to SD I/F.

>
> Or perhaps the MMC_UHS2_SUPPORT bit becomes cleared somewhere in the
> error path when first trying to initialize an UHS-II card, from
> subsequent changes?

Yes, MMC_UHS2_SUPPORT will be cleared in some cases.

>
> So, assuming that is the intent then, I am still not sure about this approach.
>
> What about if we instead always start with legacy SD initialization?
> When we have read the OCR register, via mmc_send_app_op_cond(), we can
> check if the card supports UHS-II by looking at the UHS-II Card Status
> (bit 29).

UHS-II spec recommends to detect UHS-II first.
Or in Host controller spec, section 3.13.2 card interface detection sequence,
it also starts from UHS-II path, then go SD legacy path if UHS-II
initialization fails.

The bit29 in response of ACMD41 is defined as âUHS-II Card Statusâ,
not UHS-II supported.
We have experience using this value to determine whether a card supports UHS-II,
but not every card reports if they support UHS-II by the response of
ACMD41 correctly.

>
> If it turns out that the card supports UHS-II and the host does as
> well, then we do a mmc_power_off() to completely reset the
> card/host/phy. Then we can call into a UHS-II specific path, that
> tries to power on and initialize things according to the UHS-II spec.
>
> In this way, we are going to prioritize initialization of legacy SD
> cards to remain quick, as we won't try to use UHS-II unless the card
> supports it. Moreover, I get the impression that we can keep the
> existing code more as is - and instead introduce UHS-II specifics in a
> separate path. This also also for UHS-II specific optimizations, I
> think.

Agree that we can try to keep the existing code and also need your advice/help.

>
> > +       } else {
> > +               mmc_pwrseq_pre_power_on(host);
> >
> > -       host->ios.vdd = fls(ocr) - 1;
> > -       host->ios.power_mode = MMC_POWER_UP;
> > -       /* Set initial state and call mmc_set_ios */
> > -       mmc_set_initial_state(host);
> > +               host->ios.vdd = fls(ocr) - 1;
> > +               host->ios.power_mode = MMC_POWER_UP;
> > +               /* Set initial state and call mmc_set_ios */
> > +               mmc_set_initial_state(host);
> >
> > -       mmc_set_initial_signal_voltage(host);
> > +               mmc_set_initial_signal_voltage(host);
> >
> > -       /*
> > -        * This delay should be sufficient to allow the power supply
> > -        * to reach the minimum voltage.
> > -        */
> > -       mmc_delay(host->ios.power_delay_ms);
> > -
> > -       mmc_pwrseq_post_power_on(host);
> > +               /*
> > +                * This delay should be sufficient to allow the power supply
> > +                * to reach the minimum voltage.
> > +                */
> > +               mmc_delay(host->ios.power_delay_ms);
> >
> > +               mmc_pwrseq_post_power_on(host);
> > +       }
> >         host->ios.clock = host->f_init;
> > -
> >         host->ios.power_mode = MMC_POWER_ON;
> > +
> >         mmc_set_ios(host);
> >
> > -       /*
> > -        * This delay must be at least 74 clock sizes, or 1 ms, or the
> > -        * time required to reach a stable voltage.
> > -        */
> > -       mmc_delay(host->ios.power_delay_ms);
> > +       if (host->flags & MMC_UHS2_SUPPORT)
> > +               /*
> > +                * This delay should be sufficient to allow the power supply
> > +                * to reach the minimum voltage.
> > +                */
> > +               /*  TODO: avoid an immediate value */
> > +               mmc_delay(10);
> > +       else
> > +               /*
> > +                * This delay must be at least 74 clock sizes, or 1 ms, or the
> > +                * time required to reach a stable voltage.
> > +                */
> > +               mmc_delay(host->ios.power_delay_ms);
> >  }
> >
> >  void mmc_power_off(struct mmc_host *host)
> > @@ -2307,7 +2325,11 @@ void mmc_start_host(struct mmc_host *host)
> >
> >         if (!(host->caps2 & MMC_CAP2_NO_PRESCAN_POWERUP)) {
> >                 mmc_claim_host(host);
> > -               mmc_power_up(host, host->ocr_avail);
> > +
> > +               /* Power up here will make UHS2 init ugly. */
> > +               if (!(host->caps & MMC_CAP_UHS2))
> > +                       mmc_power_up(host, host->ocr_avail);
> > +
>
> According to my suggestions, then this would not be needed.

This should not be needed. Thank you.

>
> >                 mmc_release_host(host);
> >         }
> >
> > diff --git a/drivers/mmc/core/regulator.c b/drivers/mmc/core/regulator.c
> > index 96b1d15045d6..05556225d9ac 100644
> > --- a/drivers/mmc/core/regulator.c
> > +++ b/drivers/mmc/core/regulator.c
> > @@ -247,6 +247,7 @@ int mmc_regulator_get_supply(struct mmc_host *mmc)
> >
> >         mmc->supply.vmmc = devm_regulator_get_optional(dev, "vmmc");
> >         mmc->supply.vqmmc = devm_regulator_get_optional(dev, "vqmmc");
> > +       mmc->supply.vmmc2 = devm_regulator_get_optional(dev, "vmmc2");
>
> Please move the regulator thingy here into a separate patch. Please
> make sure corresponding header file, adding the vmmc2 to it is part of
> that change as well.

Yes. will do it.

>
> >
> >         if (IS_ERR(mmc->supply.vmmc)) {
> >                 if (PTR_ERR(mmc->supply.vmmc) == -EPROBE_DEFER)
> > @@ -266,6 +267,19 @@ int mmc_regulator_get_supply(struct mmc_host *mmc)
> >                 dev_dbg(dev, "No vqmmc regulator found\n");
> >         }
> >
> > +       if (IS_ERR(mmc->supply.vmmc2)) {
> > +               if (PTR_ERR(mmc->supply.vmmc2) == -EPROBE_DEFER)
> > +                       return -EPROBE_DEFER;
> > +               dev_dbg(dev, "No vmmc2 regulator found\n");
> > +       } else {
> > +               ret = mmc_regulator_get_ocrmask(mmc->supply.vmmc2);
> > +               if (ret > 0)
> > +                       mmc->ocr_avail_uhs2 = ret;
> > +               else
> > +                       dev_warn(dev, "Failed getting UHS2 OCR mask: %d\n",
> > +                                ret);
> > +       }
> > +
> >         return 0;
> >  }
> >  EXPORT_SYMBOL_GPL(mmc_regulator_get_supply);
> > --
> > 2.27.0
> >
>
> Kind regards
> Uffe

Best regards,
Ben