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Date: Fri, 24 Jul 2020 19:11:56 +0800
From: Ben Chuang <benchuanggli@...il.com>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Adrian Hunter <adrian.hunter@...el.com>,
"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Ben Chuang <ben.chuang@...esyslogic.com.tw>,
Takahiro Akashi <takahiro.akashi@...aro.org>,
greg.tu@...esyslogic.com.tw
Subject: Re: [RFC PATCH V3 02/21] mmc: core: UHS-II support, modify power-up sequence
Hi Ulf,
On Fri, Jul 17, 2020 at 7:26 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Fri, 10 Jul 2020 at 13:07, Ben Chuang <benchuanggli@...il.com> wrote:
> >
> > From: AKASHI Takahiro <takahiro.akashi@...aro.org>
> >
> > 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@...esyslogic.com.tw>
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
> > ---
> > 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 “UHS-II Card Status”,
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
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