Re: [RFC PATCH 0/4] Describe SPI devices in the OF device tree and add mpc5200-spi driver

From: Grant Likely
Date: Fri May 16 2008 - 16:48:28 EST

On Fri, May 16, 2008 at 2:27 PM, Jon Smirl <jonsmirl@xxxxxxxxx> wrote:
> On 5/16/08, Grant Likely <grant.likely@xxxxxxxxxxxx> wrote:
>> This series is a set of changes to allow the slaves on an SPI bus to be
>> described in the OF device tree (useful in arch/powerpc) and adds a driver
>> that uses it (the Freescale MPC5200 SoC's SPI device).
> Right now we have SPI hooked up to PSC3. Hardware engineer is gone but
> I'll see if I can get him to alter things to use the SPI controller. I
> have an old mail from him where he thinks the Phytec board is missing
> a signal needed to use the SPI controller.

While I'd appreciate the testing, I suspect that you really don't want
to do that. The dedicated SPI controller isn't very good. It only
does a byte at a time and so is rather slow. A PSC is SPI mode should
be better (but I haven't tried it personally it yet).

> Is the current SPI driver working on PSC3? I have a MMC card wired up
> to it but I've never tried using it.

It should work.

> I have the MPC5200 PSC SPI driver enabled and "MMC/SD over SPI"
> enabled in my kernel. The MMC bus gets created but there aren't any
> devices on it. Do we need something in the SPI driver so that the MMC
> layer can find it?

Yes, see patch 3 in my series. the PSC SPI driver needs to do
something like this. SPI busses don't really do autodetection (but
some sub-protocols, like MMC, do IIRC).

> Are you going to keeps this as two drivers or merge them? If it is two
> drivers there should be one entry in Kconfig and two sub choices for
> the types of drivers.

It will remain as two drivers. The devices are entirely separate. I
don't think putting them under a single Kconfig is needed or a good
idea. They both depend on PPC_MPC52xx anyway so they only show up if
you're building for a 5200 platform.

Thanks for the comments.


Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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