[Arm-netbook] Testing: GPIO

Jonathan Neuschäfer j.neuschaefer at gmx.net
Fri Mar 2 22:43:42 GMT 2018


On Fri, Mar 02, 2018 at 03:26:32PM -0700, Richard Wilbur wrote:
> On Mar 1, 2018, at 20:30, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
> Sent from my iPhone
> > On Thu, Mar 1, 2018 at 9:46 PM, Richard Wilbur <richard.wilbur at gmail.com> wrote:
> >> It looks to me like the fastest way to test the GPIO lines connected
> >> on the micro-desktop board to VESA_SCL and VESA_SDA would simply be to
> >> connect a VGA monitor to the micro-desktop and make sure it is
> >> properly detected and a test image looks right on it.
> > 
> > yep, pretty much... with one slight fly in the ointment: the SCL and
> > SDA lines are straight GPIO and will need a bit-banging I2C linux
> > kernel driver.  once that's configured, doing i2cdetect _should_ be
> > enough to test the circuit, although scanning the data and running
> > read-edid on it would be awesome and amazing: it would mean being able
> > to *really* do proper VESA detection.
> Is someone already working on that?  Sounds like we need the device
> tree for the micro-desktop to be populated.  If we did it for
> micro-desktop v1.7 it would be something to build off for
> micro-desktop v1.8 and also a good place to begin for the laptop.

I'm not actively working on any of this, but I'm interested in the
devicetree side of things.

> From what I'm hearing, once the device tree is ready we could work on
> "automagically" configuring the VESA DDC driver to bit-bang the
> correct GPIO pins. Does the bit-banging VESA DDC driver exist already?
> (I wrote a bit-banging I2C driver in VxWorks at a previous position so
> the topic is not foreign.)

Mainline Linux has a driver[1] for I2C-over-GPIO. It's been there since
2.6.22, albeit initially without devicetree support, which came in 3.4.

There's also a generic devicetree binding[2] for I2C-over-GPIO in
Linux's Documentation/devicetree/bindings directory.

> If none of this is underway I'll continue mapping things out so we can
> create the device tree for the micro-desktop.  If I remember correctly
> we also should create a device tree for the DS-113 v2.7.4 and v2.7.5?

What is DS-113?

> I'd be happy to work on that if you think that is the highest priority
> right now.  It sounds like it will help both testing and deployment.

Jonathan Neuschäfer

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/i2c/busses/i2c-gpio.c
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/i2c/i2c-gpio.txt

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