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

[Y.b. Lu]

> -----Original Message-----
> From: linux-mmc-owner@xxxxxxxxxxxxxxx <linux-mmc-owner@xxxxxxxxxxxxxxx>
> On Behalf Of Ulf Hansson
> Sent: Wednesday, December 18, 2019 9:40 PM
> To: Yinbo Zhu <yinbo.zhu@xxxxxxx>; Y.b. Lu <yangbo.lu@xxxxxxx>
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>; Rasmus Villemoes
> <linux@xxxxxxxxxxxxxxxxxx>; linux-mmc@xxxxxxxxxxxxxxx; Linux Kernel
> Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
> 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@xxxxxxxxxx> wrote:
> >
> > On Wed, 4 Dec 2019 at 09:54, Rasmus Villemoes
> <linux@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
> >
> > 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.
> 

Sorry Uffe, I missed the patch since my name wasn't in TO/CC list.
I have sent out a patch for re-implementation.

Thanks!

> 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
> > >