Re: [PATCH] spi: orion: Allow specifying which HW CS to use with a GPIO CS

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

On Wed, Feb 21, 2018 at 7:58 PM, Trent Piepho <tpiepho@xxxxxxxxxx> wrote:
> On Tue, 2018-02-20 at 20:02 +0100, Jan Kundrát wrote:
>> Looking further, it seems that the CS GPIO signals are first manipulated
>> when probing for the corresponding client device. Depending on a platform
>> and its choice of a default value for the corresponding GPIO pin, this
>> might mean that a GPIO CS only gets initialized to inactive ("high" in
>> default SPI settings) too late. Other devices might have been already
>> probed for, and the CS GPIO of the "next" device might have been held
>> active ("low") during that time. How should I fix that?
>
> Design the hardware so the GPIOs are high impedance out of reset and
> put a weak pullup on each chip select line.

Most (all?) GPIO controllers come up in input mode, to avoid line conflicts.
So adding weak pull-up should be fine.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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                                -- Linus Torvalds
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