Re: SPI Framework chip select

[David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>]

On Friday 29 February 2008, Ned Forrester wrote:
> David Brownell wrote:

> > The chipselect number is always useful when the SPI bus has more
> > than one slave; it's how the slaves are distinguished.
> 
> Ahh... Here is a place where pxa2xx-spi departs from the SPI framework
> by choice.  That driver never uses spi_device.chip_select

Not directly.  Indirectly, since each chip_select is associated
with a unique pxa2xx_spi_chip.cs_control().  The chipselect number
(and signal) still distinguishes chips from each other.


> I suppose that it could alternatively been implemented by storing the
> cs_control pointers in an array during setup(), and then using the index
> in spi_device.chip_select to access the various functions.  Either way
> seems to work.

Right.  The pxa2xx_spi driver could use any scheme to manage the
chipselect signals, so long as each number maps to a unique signal.

- Dave

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