Re: [PATCH] gpio: dt-bindings: add ibm,ppc4xx-gpio binding

[Rob Herring <robh@kernel.org>]

On Thu, May 12, 2016 at 12:07:48AM +0200, Christian Lamparter wrote:
> This patch adds binding information for IBM/AMCC/APM GPIO
> Controllers of the PowerPC 4XX series and compatible SoCs.
> 
> The "PowerPC 405EP Embedded Processor Data Sheet" has the
> following to say about the GPIO controllers: "
> 
>  - Controller functions and GPIO registers are programmed
>    and accessed via memory-mapped OPB bus master accesses
> 
>  - All GPIOs are pin-shared with other functions. DCRs control
>    whether a particular pin that has GPIO capabilities acts
>    as a GPIO or is used for another purpose.
> 
>  - Each GPIO outputs is separately programmable to emulate
>    an open-drain driver (i.e. drives to zero, threestated if
>    output bit is 1)
> 
> "
> The ppc4xx_gpio.c driver is part of the platform/sysdev drivers
> in arch/powerpc/sysdev.
> 
> Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
> ---
> I looked into arch/powerpc/sysdev/ppc4xx_gpio.c driver and
> it doesn't have support for the tri-state logic (open drain
> is disabled), but the hardware would support it.
> (the #gpio-cells description suffers because of this, since
> the high-z option isn't there).
> 
> Also there's another problem: There's no DCR pinmux driver?!
> So sadly, there's not much information on how to use the DCRs
> to control the which pin is muxed to the GPIO or to a SoC
> function like the i2c.
> 
> This was all the valuable information I could find about the
> hardware, so it is included it in the binding text, even
> though there's no support for it... Is there anything else
> to add?
> ---
>  .../devicetree/bindings/gpio/ibm,ppc4xx-gpio.txt   | 24 ++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/gpio/ibm,ppc4xx-gpio.txt

Normally, we don't allow wildcards for compatible strings, but given 
this is an established binding it is okay.

Acked-by: Rob Herring <robh@kernel.org>