Subject: Re: SPI devices and OF

From: Milton Miller <[email-masked]>
Date: Thu, 5 Apr 2007 10:00:23 -0500

Ben Herrenschmidt wrote:
> Kumar Gala wrote:
>>  From explicitly board code like we do today.  I mean the mechanism
>> can very so greatly that trying to decided and come up with all
>> possible cases and somehow encoding that in the device tree isn't
>> worth the effort.  Additionally you'll still need code to handle the
>> actual chip select and I don't see how you make that generic at all.

At this point I don't think we are trying to make a generic master.  At
most we are trying to expose the spi device in a manner that can be
reused by board-specific master drivers.

>> A board designer could use I2C, GPIO, or something off an FPGA.  I
>> just dont see trying to 'encode' this in the device tree as providing
>> any real value.
>
> Or board designers can use board specific device-tree bits and board
> specific code to udnerstand them :-) That works too and can be handy if
> you have for example several versions of a board with small differences
> that you want to expose that way in the device-tree.
>
> That is, the devive-tree -can- be used to put proprietary stuff, though
> if you do so, you should try to use prefixes on your properties, like
> mycompany,xxxx

I agree with Ben here.

Asserting the chip select is the responsibility of the master driver,
and that is selected by the compatable property in the device tree
to a specific driver.

The reg property in the device node can be useful to the master driver
wihtout expressing how to assert it in the master node.

milton