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 - 17:32:31 EST

On Fri, May 16, 2008 at 3:25 PM, Jon Smirl <jonsmirl@xxxxxxxxx> wrote:
> On 5/16/08, Grant Likely <grant.likely@xxxxxxxxxxxx> wrote:
>> 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).
> What is the device tree node for PSC3 supposed to look like when it
> has both serial and spi enabled?

The *PSC3 device* cannot support both serial and SPI at the same time.
Only one mode works at a time...

However, *PSC3 pin group* has can be configured to route both the
*PSC3 device* and the *SPI device* signal out to the board at the same

Pin routing is not something that is described by the device tree.
It's viewed as a board level initialization thing, similar to how DDR
RAM initialization is viewed. Ideally, the bootloader will write the
correct value into port_config for pin routing and Linux will never
need to touch it. If the bootloader cannot be changed, then
board-specific platform code can be added to fixup the port_config
setting. However, the drivers should never touch or care about pin


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