Date:   Thu, 16 Aug 2018 14:52:41 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     jacopo mondi <jacopo@...ndi.org>
Cc:     linux-kernel@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, Jyri Sarha <jsarha@...com>,
        Daniel Vetter <daniel@...ll.ch>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>
Subject: Re: [RESEND PATCH v5 2/3] dt-bindings: display: atmel: optional
 video-interface of endpoints

On 2018-08-03 10:51, jacopo mondi wrote:
> On Fri, Aug 03, 2018 at 10:40:02AM +0200, Peter Rosin wrote:
>> On 2018-08-03 10:11, jacopo mondi wrote:
>>> Hi Peter!
>>>
>>> On Fri, Aug 03, 2018 at 09:23:07AM +0200, Peter Rosin wrote:
>>>> With bus-type/bus-width properties in the endpoint nodes, the video-
>>>> interface of the connection can be specified for cases where the
>>>> heuristic fails to select the correct output mode. This can happen
>>>> e.g. if not all RGB pins are routed on the PCB; the driver has no
>>>> way of knowing this, and needs to be told explicitly.
>>>>
>>>> This is critical for the devices that have the "conflicting output
>>>> formats" issue (SAM9N12, SAM9X5, SAMA5D3), since the most significant
>>>> RGB bits move around depending on the selected output mode. For
>>>> devices that do not have the "conflicting output formats" issue
>>>> (SAMA5D2, SAMA5D4), this is completely irrelevant.
>>>>
>>>> Acked-by: Boris Brezillon <boris.brezillon@...tlin.com>
>>>> Reviewed-by: Rob Herring <robh@...nel.org>
>>>> Signed-off-by: Peter Rosin <peda@...ntia.se>
>>>> ---
>>>>  .../devicetree/bindings/display/atmel/hlcdc-dc.txt | 26 ++++++++++++++++++++++
>>>>  1 file changed, 26 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt b/Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt
>>>> index 82f2acb3d374..9de434a8f523 100644
>>>> --- a/Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt
>>>> +++ b/Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt
>>>> @@ -15,6 +15,14 @@ Required children nodes:
>>>>   to external devices using the OF graph reprensentation (see ../graph.txt).
>>>>   At least one port node is required.
>>>>
>>>> +Optional properties in grandchild nodes:
>>>> + Any endpoint grandchild node may specify a desired video interface
>>>> + according to ../../media/video-interfaces.txt, specifically
>>>> + - bus-type: must be <0>.
>>>
>>> Is there any value in specifying this, if it has a fixed value to
>>> "autodetect"? I understand it's optional, so if nobody else objects,
>>> feels free to keep it there.
>>
>> That's just how media/video-interfaces.txt works.
>>
>> bus-type 0 means that other properties describe the bus type. In this
>> case bus-width is specified, so that means a parallel bus. But bus-width
>> has no meaning (or may not have) if bus-type is non-zero. But checking
>> that bus-type for zero in the code seemed like overkill to me since the
>> driver already knows that it is a parallel bus...
>>
> 
> Yeah, I felt like pointing that out since you're not cheking for its value,
> and that property is only used by v4l2-fwnode to handle some
> not-that-used-anymore bus as CCP2 is.
> 
>> TL;DR I'd like to keep it.
>>
> 
> Fine with me then.
> 
>>>
>>>> + - bus-width: recognized values are <12>, <16>, <18> and <24>, and
>>>> +   override any output mode selection heuristic, forcing "rgb444",
>>>> +   "rgb565", "rgb666" and "rgb888" respectively.
>>>> +
>>>>  Example:
>>>>
>>>>  	hlcdc: hlcdc@...30000 {
>>>> @@ -50,3 +58,21 @@ Example:
>>>>  			#pwm-cells = <3>;
>>>>  		};
>>>>  	};
>>>> +
>>>
>>> Two blank lines here.
>>>
>>>> +
>>>> +Example 2: With a video interface override to force rgb565; as above
>>>> +but with these changes/additions:
>>>> +
>>>> +	&hlcdc {
>>>> +		hlcdc-display-controller {
>>>> +			pinctrl-names = "default";
>>>> +			pinctrl-0 = <&pinctrl_lcd_base &pinctrl_lcd_rgb565>;
>>>> +
>>>> +			port@0 {
>>>
>>> The node has a unit address specified, you're missing a reg = <0>
>>> property (no big deal, it's an example, but the other one has it)
>>>
>>>> +				hlcdc_panel_output: endpoint@0 {
>>>
>>> Missing reg here too.
>>
>> I'll fix those (I think they appeared for the original example after I
>> wrote the patch).
>>
> 
> Ok, then please consider also describing the port@0 node cell sizes too
> since it has a child endpoint node.

Ok, I have now figured out why this was as it were, and I no longer agree
with adding the extra properties. The whole of example 2 is inside a
reference (using the &hlcdc notation) to the hlcdc node in example 1, and
therefore these "missing" properties are not missing. I think they are
just clutter that hides what is really needed/different between example 1
and 2, and apparently Boris and Rob agreed when they acked/reviewed. The
description of example 2 also clearly states that example 2 is changes
and additions on top of example 1. So, I plan to have this in the next
iteration:

	&hlcdc {
		hlcdc-display-controller {
			pinctrl-names = "default";
			pinctrl-0 = <&pinctrl_lcd_base &pinctrl_lcd_rgb565>;

			port@0 {
				hlcdc_panel_output: endpoint@0 {
					bus-width = <16>;
				};
			};
		};
	};

Jacopo, please let me know if you want me to keep your review tag anyway...


>> Cheers,
>> Peter
>>
>>> Minors apart:

...because I interpret this to mean that I could add your tag if I made the
changes you suggested. Or did it mean that I could add your tag regardless
because the issues were minor?

Cheers,
Peter

>>>
>>> Reviewed-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
>>>
>>> Thanks
>>>    j
>>>
>>>> +					bus-type = <0>;
>>>> +					bus-width = <16>;
>>>> +				};
>>>> +			};
>>>> +		};
>>>> +	};
>>>> --
>>>> 2.11.0
>>>>
>>

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