linux-kernel - Re: [RFC PATCH V3 04/21] mmc: core: UHS-II support, try to select UHS-II interface

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Message-ID: <CAPDyKFoL8Yh_SJSw56kQsFBRE64oRGTnyzgvOm__-1f+Cvxpzw@mail.gmail.com>
Date:   Fri, 21 Aug 2020 14:25:55 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Ben Chuang <benchuanggli@...il.com>
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 04/21] mmc: core: UHS-II support, try to select
 UHS-II interface

[...]

> > > @@ -2300,6 +2304,33 @@ void mmc_rescan(struct work_struct *work)
> > >                 goto out;
> > >         }
> > >
> > > +       if (host->caps & MMC_CAP_UHS2) {
> > > +               /*
> > > +                * Start to try UHS-II initialization from 52MHz to 26MHz
> > > +                * (RCLK range) per spec.
> > > +                */
> > > +               for (i = 0; i < ARRAY_SIZE(uhs2_freqs); i++) {
> > > +                       unsigned int freq = uhs2_freqs[i];
> > > +                       int err;
> > > +
> > > +                       err = mmc_uhs2_rescan_try_freq(host,
> > > +                                                      max(freq, host->f_min));
> > > +                       if (!err) {
> > > +                               mmc_release_host(host);
> > > +                               goto out;
> > > +                       }
> > > +
> > > +                       if (err == UHS2_PHY_INIT_ERR)
> > > +                               /* UHS2 IF detect or Lane Sync error.
> > > +                                * Try legacy interface.
> > > +                                */
> > > +                               break;
> > > +
> > > +                       if (freq <= host->f_min)
> > > +                               break;
> > > +               }
> >
> > Assuming we change the initialization order, trying to initialize the
> > legacy SD interface first to figure out if UHS-II is supported, then I
> > think we should be able to move the entire code above into a the
> > UHS-II specific code/path.
>
> If the host tries to use the SD interface first,
> some failure status needs to be considered.
>
> For example, first run in SD mode, try UHS-II interface failure,
>  and then return to SD flow again.
> I don't know a good way to go back to SD flow again.

Right, a re-try path for the legacy SD interface is a very good idea!
However, I don't think the initial support for UHS-II needs to cover
it. Instead we can add that on top, don't you think?

As a matter of fact, we could even use something like that for
different legacy SD speed modes. For example, if UHS-I SDR104 fails we
could try with UHS-I SDR25.

>
> >
> > > +       }
> > > +
> > >         for (i = 0; i < ARRAY_SIZE(freqs); i++) {
> > >                 unsigned int freq = freqs[i];
> > >                 if (freq > host->f_max) {
> > > diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
> > > index 5a2210c25aa7..c5b071bd98b3 100644
> > > --- a/drivers/mmc/core/sd.c
> > > +++ b/drivers/mmc/core/sd.c
> > > @@ -901,6 +901,20 @@ int mmc_sd_setup_card(struct mmc_host *host, struct mmc_card *card,
> > >                 err = mmc_read_switch(card);
> > >                 if (err)
> > >                         return err;
> > > +               if (host->flags & MMC_UHS2_INITIALIZED) {
> >
> > Rather than using host->flags, to tweak the behavior of
> > mmc_sd_setup_card() to support UHS-II, I would prefer to give
> > mmc_sd_setup_card() a new in-parameter that it can look at instead.
>
> Do you mean that adding a new in-parameter to mmc_sd_setup_card() likes this
> mmc_sd_setup_card(struct mmc_host *, struct mmc_card *, boot reinit,
> boot uhsii); ?

Correct.

[...]

Looks like we have covered most of the review for the mmc core
changes. But please tell me, if there is anything else you want me to
look at - at any time. Otherwise I am deferring to wait for a new
version of the series.

If I get some time, I may start to help with hacking some code.
Perhaps I can do some preparations, so it makes it easier for you to
add the UHS-II specific code. If so, I will let you know about it, of
course.

When it comes to the changes to SDHCI, I am relying on Adrian to give
his opinions.

Kind regards
Uffe