Re: SDHI polling

[Simon Horman <horms@verge.net.au>]

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.

If the answer is no then I will need to deviate from my
based-on-MMCIF-MMC-boot plan.