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

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Date:	Fri, 16 May 2008 14:48:16 -0600
From:	"Grant Likely" <grant.likely@...retlab.ca>
To:	"Jon Smirl" <jonsmirl@...il.com>
Cc:	linuxppc-dev@...abs.org, spi-devel-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, dbrownell@...rs.sourceforge.net,
	fabrizio.garetto@...il.com
Subject: Re: [RFC PATCH 0/4] Describe SPI devices in the OF device tree and add mpc5200-spi driver

On Fri, May 16, 2008 at 2:27 PM, Jon Smirl <jonsmirl@...il.com> wrote:
> On 5/16/08, Grant Likely <grant.likely@...retlab.ca> 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.

Cheers,
g.

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