[PATCH 27/32] gpio: Add support for the FXL6408 GPIO expander.

Eric Anholt eric at anholt.net
Mon Jun 6 16:50:31 PDT 2016

Gerd Hoffmann <kraxel at redhat.com> writes:

> From: Eric Anholt <eric at anholt.net>
> This commit needs to be split up and cleaned up.  Also we should add
> interrupt support before pushing upstream.
> Signed-off-by: Eric Anholt <eric at anholt.net>

OK, I've confirmed with the firmware maintainers: We really can't drive
this natively from Linux.  The firmware is polling one of the fxl6408's
pins 10 times a second for detecting under-voltage, so if we also try to
drive it we'll end up smashing each others' I2C transactions.  We'll
need to do a GPIO driver using the GET/SET_GPIO_STATE firmware calls,
instead.  Unfortunately, we don't have a direction-setting API for that
at the moment, but it'll at least let us read the HDMI HPD signal.
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