linux-kernel - Re: [PATCH] mmc: sdhci-of-esdhc: Revert "mmc: sdhci-of-esdhc: add erratum A-009204 support"

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Date:   Wed, 18 Dec 2019 14:39:46 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Yinbo Zhu <yinbo.zhu@....com>, Yangbo Lu <yangbo.lu@....com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: sdhci-of-esdhc: Revert "mmc: sdhci-of-esdhc: add
 erratum A-009204 support"

Yinbo, Yangbo

On Tue, 10 Dec 2019 at 10:51, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Wed, 4 Dec 2019 at 09:54, Rasmus Villemoes <linux@...musvillemoes.dk> wrote:
> >
> > This reverts commit 5dd195522562542bc6ebe6e7bd47890d8b7ca93c.
> >
> > First, the fix seems to be plain wrong, since the erratum suggests
> > waiting 5ms before setting setting SYSCTL[RSTD], but this msleep()
> > happens after the call of sdhci_reset() which is where that bit gets
> > set (if SDHCI_RESET_DATA is in mask).
> >
> > Second, walking the whole device tree to figure out if some node has a
> > "fsl,p2020-esdhc" compatible string is hugely expensive - about 70 to
> > 100 us on our mpc8309 board. Walking the device tree is done under a
> > raw_spin_lock, so this is obviously really bad on an -rt system, and a
> > waste of time on all.
> >
> > In fact, since esdhc_reset() seems to get called around 100 times per
> > second, that mpc8309 now spends 0.8% of its time determining that
> > it is not a p2020. Whether those 100 calls/s are normal or due to some
> > other bug or misconfiguration, regularly hitting a 100 us
> > non-preemptible window is unacceptable.
> >
> > Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
>
> Applied for fixes and by adding a stable tag, thanks!

Just wanted to highlight, that $subject patch has been applied for
fixes, which means we need a new fix the errata A-009204.

Rasmus kind of already hinted on how this could be fixed in a better
way, hope this helps.

Kind regards
Uffe

> > ---
> >
> > The errata sheet for mpc8309 also mentions A-009204, so I'm not at all
> > opposed to having a fix for that. But it needs to be done properly
> > without causing a huge performance or latency impact. We should
> > probably just add a bit to struct sdhci_esdhc which gets initialized
> > in esdhc_init.
> >
> >  drivers/mmc/host/sdhci-of-esdhc.c | 3 ---
> >  1 file changed, 3 deletions(-)
> >
> > diff --git a/drivers/mmc/host/sdhci-of-esdhc.c b/drivers/mmc/host/sdhci-of-esdhc.c
> > index 5cca3fa4610b..7f87a90bf56a 100644
> > --- a/drivers/mmc/host/sdhci-of-esdhc.c
> > +++ b/drivers/mmc/host/sdhci-of-esdhc.c
> > @@ -764,9 +764,6 @@ static void esdhc_reset(struct sdhci_host *host, u8 mask)
> >         sdhci_writel(host, host->ier, SDHCI_INT_ENABLE);
> >         sdhci_writel(host, host->ier, SDHCI_SIGNAL_ENABLE);
> >
> > -       if (of_find_compatible_node(NULL, NULL, "fsl,p2020-esdhc"))
> > -               mdelay(5);
> > -
> >         if (mask & SDHCI_RESET_ALL) {
> >                 val = sdhci_readl(host, ESDHC_TBCTL);
> >                 val &= ~ESDHC_TB_EN;
> > --
> > 2.23.0
> >