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

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Message-ID: <20200918063843.GA46229@laputa>
Date:   Fri, 18 Sep 2020 15:38:43 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Ben Chuang <benchuanggli@...il.com>, ulf.hansson@...aro.org,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        ben.chuang@...esyslogic.com.tw, greg.tu@...esyslogic.com.tw
Subject: Re: [RFC PATCH V3 12/21] mmc: sdhci: UHS-II support, add hooks for
 additional operations

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?
        -> Ben

I also wonder why we need spin locks in uhs2_do_set_ios() while
not in sdhci_set_ios().

        -> Ben

-Takahiro Akashi