linux-kernel - Re: [RFC PATCH V3 12/21] mmc: sdhci: UHS-II support, add hooks for additional operations

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Date:   Fri, 25 Sep 2020 15:55:18 +0800
From:   Ben Chuang <benchuanggli@...il.com>
To:     AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Ben Chuang <benchuanggli@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ben Chuang <ben.chuang@...esyslogic.com.tw>,
        greg.tu@...esyslogic.com.tw, Renius.Chen@...esyslogic.com.tw
Subject: Re: [RFC PATCH V3 12/21] mmc: sdhci: UHS-II support, add hooks for
 additional operations

Takahiro,

On Thu, Sep 24, 2020 at 5:57 PM AKASHI Takahiro
<takahiro.akashi@...aro.org> wrote:
>
> Ben,
>
> On Fri, Sep 18, 2020 at 06:50:24PM +0800, Ben Chuang wrote:
> > On Fri, Sep 18, 2020 at 2:38 PM AKASHI Takahiro
> > <takahiro.akashi@...aro.org> wrote:
> > >
> > > Adrian, Ben,
> > >
> > > Regarding _set_ios() function,
> > >
> > > On Fri, Aug 21, 2020 at 05:08:32PM +0300, Adrian Hunter wrote:
> > > > On 10/07/20 2:10 pm, Ben Chuang wrote:
> > > > > From: Ben Chuang <ben.chuang@...esyslogic.com.tw>
> > > > >
> > > > > In this commit, UHS-II related operations will be called via a function
> > > > > pointer array, sdhci_uhs2_ops, in order to make UHS-II support as
> > > > > a kernel module.
> > > > > This array will be initialized only if CONFIG_MMC_SDHCI_UHS2 is enabled
> > > > > and when the UHS-II module is loaded. Otherwise, all the functions
> > > > > stay void.
> > > > >
> > > > > Signed-off-by: Ben Chuang <ben.chuang@...esyslogic.com.tw>
> > > > > Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
> > >
> > >   (snip)
> > >
> > > > > @@ -2261,6 +2324,7 @@ void sdhci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
> > > > >  {
> > > > >     struct sdhci_host *host = mmc_priv(mmc);
> > > > >     u8 ctrl;
> > > > > +   u16 ctrl_2;
> > > > >
> > > > >     if (ios->power_mode == MMC_POWER_UNDEFINED)
> > > > >             return;
> > > > > @@ -2287,6 +2351,10 @@ void sdhci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
> > > > >             sdhci_enable_preset_value(host, false);
> > > > >
> > > > >     if (!ios->clock || ios->clock != host->clock) {
> > > > > +           if (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> > > > > +               ios->timing == MMC_TIMING_UHS2)
> > > > > +                   host->timing = ios->timing;
> > > > > +
> > > > >             host->ops->set_clock(host, ios->clock);
> > > > >             host->clock = ios->clock;
> > > > >
> > > > > @@ -2308,6 +2376,18 @@ void sdhci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
> > > > >     else
> > > > >             sdhci_set_power(host, ios->power_mode, ios->vdd);
> > > > >
> > > > > +   /* 4.0 host support */
> > > > > +   if (host->version >= SDHCI_SPEC_400) {
> > > > > +           /* UHS2 Support */
> > > > > +           if (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> > > > > +               host->mmc->flags & MMC_UHS2_SUPPORT &&
> > > > > +               host->mmc->caps & MMC_CAP_UHS2) {
> > > > > +                   if (sdhci_uhs2_ops.do_set_ios)
> > > > > +                           sdhci_uhs2_ops.do_set_ios(host, ios);
> > > > > +                   return;
> > > > > +           }
> > > > > +   }
> > > > > +
> > > >
> > > > Please look at using existing callbacks instead, maybe creating uhs2_set_ios(), uhs2_set_clock(), uhs2_set_power()
> > >
> > > I think that we will create uhs2_set_ios() (and uhs2_set_power()
> > > as we discussed on patch#15/21), but not uhs_set_clock().
> > >
> > > Since we have a hook only in struct mmc_host_ops, but not in struct
> > > sdhci_ops, all the drivers who want to support UHS-II need to
> > > set host->mmc_host_ops->set_ios to sdhci_uhs2_set_ios explicitly
> > > in their own init (or probe) function.
> > > (Again, sdhci_uhs2_set_ios() seems to be generic though.)
> > >
> > > Is this okay for you?
> > >         -> Adrian
> > >
> > > During refactoring the code, I found that sdhci_set_power() is called
> > > twice in sdhci_set_ios():
> > >         sdhci_set_ios(host, power_mode, vdd1, -1); in sdhci_set_ios(), and
> > >         sdhci_set_ios(host, power_mode, vdd1, vdd2) in ush2_do_set_ios()
> > >
> > > Can you please confirm that those are redundant?
> >
> > Yes, uhs2 set power is independent with uhs1.
> > But set  uhs2 power process  should meet  uhs2 spec.
>
> Can you elaborate a bit more about the last sentence, please?
>
> What I meant above is that
>          sdhci_set_ios(host, power_mode, vdd1, vdd2) in ush2_do_set_ios()
>
> this code will 'set_power' both vdd and vdd2 anyway and so
>          sdhci_set_ios(host, power_mode, vdd1, -1); in sdhci_set_ios(), and
> is just redundant.
>

Yes, for uhs-2 flow,  sdhci_set_ios(host, power_mode, vdd1, -1) is redundant.

>
> > >         -> Ben
> > >
> > > I also wonder why we need spin locks in uhs2_do_set_ios() while
> > > not in sdhci_set_ios().
> >
> > You can check if  spin locks in uhs2_do_set_ios() is necessary.
>
> I'm asking you.
>
> While calling set_ios() doesn't require spin locks, are you aware of
> any cases where we need spin locks in calling set_ios() for uhs-2?
> (I mean that callers/contexts are the same either for uhs or uhs-2.)

I agree that it can be removed. I just didn't modify intel's original codes.

>
> -Takahiro Akashi
>
> > If set/clear irq can be execute safely without spin locks, you can
> > remove spin locks.
> >
> > >
> > >         -> Ben
> > >
> > > -Takahiro Akashi