[PATCH 5/8] gpio: 74x164: Add output pin support

Thomas Petazzoni thomas.petazzoni at free-electrons.com
Wed Sep 5 08:29:52 EDT 2012

Le Wed, 5 Sep 2012 14:22:44 +0200,
Eric Bénard <eric at eukrea.com> a écrit :

> > > OK that's exactly what I was thinking to ;-)
> > 
> > Good. So, do you think it's reasonable to use the STCP as a chip-select
> > for this device?
> in your case maybe but that really depends on how the chip is wired to
> the CPU so I'm not sure that can be a generic choice.

I'm not sure to see how this chip could be wired differently to the
CPU. The CPU must do a low-to-high transition on STCP to get the values
out from the internal register.

So, in other words, we don't know how to choose between:

 *) Keep the current solution Maxime has implemented, where we have a
    specific latch GPIO property in the Device Tree for this 74HC595,
    and the 74HC595 driver is responsible for toggling this GPIO when

 *) Use the internal SPI controller logic to control this pin as a
    chip-select, and therefore get rid of Maxime's code with the
    specific latch GPIO property in the Device Tree.


Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.

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