Re: [PATCH 2/2] dt-bindings: simplefb-sunxi: Add sunxi simplefb extensions

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 11/18/2014 09:47 AM, Ian Campbell wrote:
> On Tue, 2014-11-18 at 09:15 +0100, Hans de Goede wrote:
>> Hi,
>>
>> On 11/17/2014 04:55 PM, Maxime Ripard wrote:
>>> On Mon, Nov 17, 2014 at 01:39:18PM +0000, Grant Likely wrote:
>>>> On Mon, Nov 17, 2014 at 12:47 PM, Maxime Ripard
>>>> <maxime.ripard@free-electrons.com> wrote:
>>>>> On Mon, Nov 17, 2014 at 12:34:46PM +0100, Hans de Goede wrote:
>>>>>> If pre-filled framebuffer nodes are used, the firmware may need extra
>>>>>> properties to find the right node. This documents the properties to use
>>>>>> for this on sunxi platforms.
>>>>>>
>>>>>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>>>>>> ---
>>>>>>  .../bindings/video/simple-framebuffer-sunxi.txt    | 33 ++++++++++++++++++++++
>>>>>>  1 file changed, 33 insertions(+)
>>>>>>  create mode 100644 Documentation/devicetree/bindings/video/simple-framebuffer-sunxi.txt
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/video/simple-framebuffer-sunxi.txt b/Documentation/devicetree/bindings/video/simple-framebuffer-sunxi.txt
>>>>>> new file mode 100644
>>>>>> index 0000000..84ca264
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/video/simple-framebuffer-sunxi.txt
>>>>>> @@ -0,0 +1,33 @@
>>>>>> +Sunxi specific Simple Framebuffer bindings
>>>>>> +
>>>>>> +This binding documents sunxi specific extensions to the simple-framebuffer
>>>>>> +bindings. The sunxi simplefb u-boot code relies on the devicetree containing
>>>>>> +pre-populated simplefb nodes.
>>>>>> +
>>>>>> +These extensions are intended so that u-boot can select the right node based
>>>>>> +on which pipeline and output is being used. As such they are solely intended
>>>>>> +for firmware / bootloader use, and the OS should ignore them.
>>>>>> +
>>>>>> +Required properties:
>>>>>> +- compatible: "sunxi,framebuffer"
>>>>>> +- sunxi,pipeline:
>>>>>> +  <0> for the de_be0 -> lcdc0 -> output pipeline
>>>>>> +  <1> for the de_be1 -> lcdc1 -> output pipeline
>>>>>> +- sunxi,output: One of: "hdmi", "lcd", "vga", and "composite"
>>>>>> +
>>>>>> +Example:
>>>>>> +
>>>>>> +chosen {
>>>>>> +     #address-cells = <1>;
>>>>>> +     #size-cells = <1>;
>>>>>> +     ranges;
>>>>>> +
>>>>>> +     framebuffer@0 {
>>>>>> +             compatible = "sunxi,framebuffer", "simple-framebuffer";
>>>>>> +             sunxi,pipeline = <0>;
>>>>>> +             sunxi,output = "hdmi";
>>>>>> +             clocks = <&pll5 1>, <&ahb_gates 36>, <&ahb_gates 43>,
>>>>>> +                      <&ahb_gates 44>;
>>>>>
>>>>> If we're going that way, then maybe having to specify clock-names
>>>>> would be better in order to know which clock is what?
>>>>
>>>> I wouldn't go that way with this binding since the driver has no need
>>>> to differentiate between the clocks, and driver authors shouldn't be
>>>> encouraged to do so. The purpose of the clocks in this node is only
>>>> for itemizing dependencies, not for how to configure the clocks.
>>>> Firmware shouldn't care at all about the clocks list, it only needs to
>>>> find the correct pre-populated node to fill in and enable.
>>>
>>> Well, if we want to play the "DT as an ABI" stuff, you have no
>>> guarantee that in the future, simplefb will still be the driver bound
>>> to "sunxi,framebuffer"
>>
>> Huh? We do have that guarantee, or at least that a simplefb bindings
>> compatible driver is, the "sunxi,framebuffer" bindings live in:
>>
>> Documentation/devicetree/bindings/video/simple-framebuffer-sunxi.txt
>>
>> With the filename already being a big hint, further more it states that:
>>
>> "This binding documents sunxi specific extensions to the simple-framebuffer
>> bindings. The sunxi simplefb u-boot code relies on the devicetree containing
>> pre-populated simplefb nodes.
>>
>> These extensions are intended so that u-boot can select the right node based
>> on which pipeline is being used. As such they are solely intended for
>> firmware / bootloader use, and the OS should ignore them."
> 
> There may be an argument here for using the slightly redundant compat
> string "allwinner,simple-framebuffer" in order to reinforce that this is
> an extension to simple-framebuffer, as opposed to a binding for a
> completely separate "non-simple" sunxi framebuffer driver which I think
> is what Maxime may be imagining.
> 
> Alternatively (or as well) perhaps these extension should be a series of
> extensions (one per platform) described in "appendices" of the main
> simple-framebuffer.txt. I know Grant expressed a preference for a
> separate document though and I think just using the more expressive name
> above would be sufficient, but thought I'd mention it as a possible
> option.

That is a good suggestion, as discussed on irc, lets go with that.

Regards,

Hans