Re: [PATCH v2 15/18] drivers/fsi: Add documentation for GPIO based FSI master

[Christopher Bostic <christopher.lee.bostic@gmail.com>]

On Wed, Jan 18, 2017 at 3:57 PM, Rob Herring <robh@kernel.org> wrote:
> On Thu, Jan 12, 2017 at 04:35:43PM -0600, christopher.lee.bostic@gmail.com wrote:
>> From: Chris Bostic <cbostic@us.ibm.com>
>>
>> Define the device tree bindings for the GPIO master type.
>>
>> Signed-off-by: Chris Bostic <cbostic@us.ibm.com>
>>
>> ---
>>
>> V2 - Break out this documentation update from the code implementing
>>      The GPIO master function.
>>
>>    - Move the documentation to an earlier patch than the code
>>      implementing the function.
>>
>>    - Document all 'compatible' strings used in the series.
>>
>>    - Write binding document in terms of hardware, not software.
>>
>>    - Elaborate on what a GPIO based FSI master is versus a non
>>      GPIO based master.
>>
>>    - Give a more detailed description of what each pin in the GPIO
>>      FSI master is to be used for.
>>
>>    - Re-order compatible strings in example so that most specific
>>      comes first.
>>
>>    - Indicate the proper order each pin should be initialized.
>>
>>    - Fix an unmatched '>' bracket in the example for binding.
>>
>>    - Bracket each element of the example list items individually.
>> ---
>>  .../devicetree/bindings/fsi/fsi-master-gpio.txt    | 71 ++++++++++++++++++++++
>>  1 file changed, 71 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/fsi/fsi-master-gpio.txt
>>
>> diff --git a/Documentation/devicetree/bindings/fsi/fsi-master-gpio.txt b/Documentation/devicetree/bindings/fsi/fsi-master-gpio.txt
>> new file mode 100644
>> index 0000000..5d589bf
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/fsi/fsi-master-gpio.txt
>> @@ -0,0 +1,71 @@
>> +Device-tree bindings for FSI master implemented with GPIO
>> +---------------------------------------------------------
>> +
>> +Typically a FSI master is defined in hardware with output control
>> +lines designated for Enable, Data, Clock, etc..  In the case of
>> +a 'GPIO FSI master', however, it may be the case that there is no
>> +such master defined in hardware and must be implemented in standard
>> +GPIO to interact with its slaves.  In this 'virtual' FSI master
>> +case the GPIO pins representing clk and data are directly
>> +connected to the slaves.
>> +
>> +The GPIO FSI master node
>> +-------------------------
>> +This node describes a FSI master implmented with GPIO.
>> +Required property:
>> +     compatible = "ibm,fsi-master-gpio"
>
> Generally, we don't have a vendor prefix for GPIO based implementations.
>

Hi Rob

Will make the change in the next revision (v4).

>> +
>> +The standard FSI master node
>> +----------------------------
>> +This node describes a FSI master implmemented fully in hardware
>> +with dedicated input/output pins required for its function (i.e.
>> +not using generic GPIO pins).
>> +Required property:
>> +     compatible = "ibm,fsi-master"
>
> This and GPIO binding should be in 2 docs.
>

Will separate out.

>> +
>> +
>> +GPIO FSI master property/pin descriptions
>> +------------------------------------------
>> +clk -        The master controlled clock line that indicates to the
>> +     slave when to read in or send out new data - required.
>> +data -       The serial data line containing information to be sent or
>> +     received by the master.  This line is bi-directional.  During
>> +     command phase the master controls the line and when a response
>> +     is required the slave takes control - required.
>> +enable - Controls power state of data line - optional.
>> +trans - Voltage translator control. In some applications the data line
>> +     must have its signal levels altered by a translator. If this is
>> +     necessary then control of signal direction is managed via this
>> +     line - optional.
>> +mux -        Multiplexor control.  This activates/deactivates the data line
>> +     in cases where it is one of many possible selections via mux -
>> +     optional.
>
> Combine these descriptions and the property names, grouped as below.
>

Will update.

>> +
>> +Required properties:
>> +     - compatible = "ibm,fsi-master-gpio";
>> +     - clk-gpios;
>> +     - data-gpios;
>> +
>> +Optional properties:
>> +     - enable-gpios;
>> +     - trans-gpios;
>> +     - mux-gpios;
>> +
>> +Order of property activation:
>> +1. clk
>> +2. data
>> +3. trans
>> +4. enable
>> +5. mux
>> +
>> +
>> +Example:
>> +
>> +fsi-master {
>> +     compatible = "ibm,fsi-master-gpio", "ibm,fsi-master";
>
> From the description, these should be mutually exclusive.

Will change.

Thanks for your input.

>
>> +     clk-gpios = <&gpio 0>, <&gpio 6>;
>> +     data-gpios = <&gpio 1>, <&gpio 7>;
>> +     enable-gpios = <&gpio 2>, <&gpio 8>;
>> +     trans-gpios = <&gpio 3>, <&gpio 9>;
>> +     mux-gpios = <&gpio 4>, <&gpio 10>;
>> +}
>> --
>> 1.8.2.2
>>