Date: Sun, 6 Sep 2009 15:25:37 +0200
From: Pierre Ossman <pierre@ossman.eu>
To: Matthieu CASTET <matthieu.castet@parrot.com>
Cc: sdhci-devel@lists.ossman.eu,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: sdhci can turn off irq up to 200 ms
Message-ID: <20090906152537.15303d69@mjolnir.ossman.eu>
In-Reply-To: <4A55C631.7030103@parrot.com>
References: <4A4B6184.7000903@parrot.com>
	<4A55C631.7030103@parrot.com>
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On Thu, 9 Jul 2009 12:28:01 +0200
Matthieu CASTET <matthieu.castet@parrot.com> wrote:

> Matthieu CASTET a =C3=A9crit :
> > Hi,
> >=20
> > sdhci code got tasklets (sdhci_tasklet_card and sdhci_tasklet_finish),
> > that does :
> > {
> > spin_lock_irqsave
> >=20
> > if (cond) {
> > sdhci_reset
> > sdhci_reset
> > }
> >=20
> > spin_unlock_irqrestore
> > }
> >=20
> > The problem is that sdhci_reset [1] does busy pooling on a register up
> > to a timeout of 100 ms.
> > That's not low latency friendly.
> >=20
> > On our system, we saw that sdhci_reset take 1 ms. That should be because
> > we enter in mdelay, even if the hardware clears the bit faster.
> > I wonder why there is an mdelay(1). Using cpu_relax and
> > time_is_after_jiffies should make sdhci_reset faster.
> >=20
> In case somebody cares, here a patch that reduce on our hardware
> sdhci_reset from 1 ms to 30 us.
>=20

I seem to recall having problems with jiffies not updating with those
locks held (or perhaps it was when inside the isr).

What arch have you been testing this on?

Rgds
--=20
     -- Pierre Ossman

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