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From: Kumar Gala <galak@kernel.crashing.org>
Subject: Re: [PATCH] Add QE device tree definition
Date: Fri, 30 Jun 2006 00:37:13 -0500
To: Li Yang-r58472 <LeoLi@freescale.com>
Cc: linuxppc-dev@ozlabs.org
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>>>>
>>>>>>> +   2) SPI (Serial Peripheral Interface)
>>>>>>> +
>>>>>>> +   Required properties:
>>>>>>> +   - device_type : should be "spi".
>>>>>>> +   - compatible : should be "fsl_spi".
>>>>>>> +   - mode : the spi operation mode, it can be "cpu" or "qe".
>>>>>>
>>>>>> What does it mean for the spi to be in "qe" mode?
>>>>> That means:
>>>>> The SPI can operate in QE mode or in CPU mode. In QE mode SPI is
>>>>> compatible to the MPC826x SPI, and is controlled by QE RISC. In  
>>>>> CPU
>>>>> mode, the SPI is controlled wholly by the CPU without any QE RISC
>>>>> intervention.
>>>>
>>>> In QE mode does software get involved at all?
>>>
>>> Yes, of course.  The driver needs to do initialization, and deal
>>> with the BDs.
>>
>> So what exactly does the QE do in this mode?
>
> Just like CPM.  Driver only deal with buffer and buffer  
> descriptor.  And QE will take care of the other things.
> While in CPU mode, it is up to the CPU to pack and unpack the  
> receive/transmit frames.  And tx/rx through data registers.

Ohh, so CPU mode matches the 834x then, and QE mode matches 82xx/CPM.

Has anyone looked at extending the 834x driver that is in the tree  
now for using descriptors for QE/82xx?

- k