From: Simon Horman <horms@verge.net.au>
To: linux-sh@vger.kernel.org
Subject: Re: SDHI polling
Date: Mon, 27 Dec 2010 01:13:38 +0000 [thread overview]
Message-ID: <20101227011336.GA15786@verge.net.au> (raw)
In-Reply-To: <20101226224506.GD21535@verge.net.au>
On Mon, Dec 27, 2010 at 09:57:50AM +0900, Magnus Damm wrote:
> On Mon, Dec 27, 2010 at 9:23 AM, Simon Horman <horms@verge.net.au> wrote:
> > On Mon, Dec 27, 2010 at 07:59:15AM +0900, Magnus Damm wrote:
> >> Hi Simon,
> >>
> >> On Mon, Dec 27, 2010 at 7:45 AM, Simon Horman <horms@verge.net.au> wrote:
> >> > I have it in mind to run the SDHI hardware block in some sort of
> >> > polling mode - that is, with interrupts disabled - during early
> >> > boot. Does this make any sense?
> >>
> >> I guess it depends on how early you mean. =)
> >>
> >> Usually you want to make use of interrupts if they are available, but
> >> for really early code there is no interrupt support. So the in-kernel
> >> early printk support is implemented without any interrupts for
> >> instance. At least this is true for the SCIF driver used by SH and
> >> SH-Mobile / R-Mobile, pretty sure it applies to other hardware
> >> platforms as well.
> >>
> >> As for the SDHI version of the MMC loader, I think you should do the
> >> same as the MMCIF loader that is present in
> >> include/linux/mmc/sh_mmcif.h. As you know it gets compiled into a
> >> separate image together with the rest of the zImage loader. No
> >> interrupt handling is available in that code, so just implementing
> >> things using polling mode is good enough.
> >>
> >> I'm not 100% sure about U-boot these days, but I wouldn't be surprised
> >> if many boot loaders only implement polling.
> >
> > My plan is to implement the SDHI version of the MMC loader along
> > the same lines of the MMCIF version. That plan involves early boot
> > where there are no interrupts.
> >
> > My question was really to ask if from a hardware point of view it is
> > possible/reasonable to read from an MMC card using SHDI without interrupts.
> > I gather that the answer is yes.
>
> I believe that is possible, yes. Maybe you can ask around for some
> out-of-tree SDHI u-boot excellence to use as an example. I imagine
> such code may use polling. =)
Good thinking.
next prev parent reply other threads:[~2010-12-27 1:13 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-26 22:45 SDHI polling Simon Horman
2010-12-26 22:59 ` Magnus Damm
2010-12-26 23:24 ` Paul Mundt
2010-12-26 23:34 ` Magnus Damm
2010-12-27 0:10 ` Paul Mundt
2010-12-27 0:23 ` Simon Horman
2010-12-27 0:57 ` Magnus Damm
2010-12-27 1:03 ` Magnus Damm
2010-12-27 1:13 ` Simon Horman [this message]
2010-12-27 1:36 ` Paul Mundt
2010-12-27 1:44 ` Simon Horman
2010-12-27 1:47 ` Magnus Damm
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