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Subject: Re: [RESEND PATCH v5 2/3] dt-bindings: display: atmel: optional
 video-interface of endpoints
To:     jacopo mondi <jacopo@jmondi.org>
Cc:     linux-kernel@vger.kernel.org,
        Boris Brezillon <boris.brezillon@bootlin.com>,
        David Airlie <airlied@linux.ie>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Nicolas Ferre <nicolas.ferre@microchip.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, Jyri Sarha <jsarha@ti.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrzej Hajda <a.hajda@samsung.com>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        Jacopo Mondi <jacopo+renesas@jmondi.org>
References: <20180803072308.14962-1-peda@axentia.se>
 <20180803072308.14962-3-peda@axentia.se> <20180803081128.GA4528@w540>
From:   Peter Rosin <peda@axentia.se>
Organization: Axentia Technologies AB
Message-ID: <6fe3e84e-bd9d-0894-df8b-1b40c0f9477d@axentia.se>
Date:   Fri, 3 Aug 2018 10:40:02 +0200
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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@bootlin.com>
>> Reviewed-by: Rob Herring <robh@kernel.org>
>> Signed-off-by: Peter Rosin <peda@axentia.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...

TL;DR I'd like to keep it.

> 
>> + - 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@f0030000 {
>> @@ -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).

Cheers,
Peter

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