linux-kernel - Re: [PATCH 2/2] arm64: dts: exynos: Remove unneeded DSI and DECON address/size cells in Exynos5433

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Date:   Thu, 21 Jun 2018 07:59:20 +0200
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Kukjin Kim <kgene@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: dts: exynos: Remove unneeded DSI and DECON
 address/size cells in Exynos5433

On 20.06.2018 21:34, Krzysztof Kozlowski wrote:
> On Tue, Jun 19, 2018 at 09:59:04AM +0200, Krzysztof Kozlowski wrote:
>> On 19 June 2018 at 09:26, Marek Szyprowski <m.szyprowski@...sung.com> wrote:
>>> Hi Krzysztof,
>>>
>>> On 2018-06-18 19:42, Krzysztof Kozlowski wrote:
>>>> The decon, decon_tv and dsi nodes have only one child port so
>>>> address/size mappings are not necessary.  This fixes DTC warnings like:
>>>>
>>>>      Warning (graph_child_address): /soc/decon@...00000/ports:
>>>>          graph node has single child node 'port@0', #address-cells/#size-cells are not necessary
>>>>
>>>> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
>>> Works fine with current Exynos DRM Decon/MIC/DSI drivers.
>>>
>>> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
>> Thanks for review and testing!
> I have second thoughs whether this patch is correct. AFAIU, the drivers
> get the remote endpoints by reg==0 (for example the
> of_graph_get_remote_node() in exynos_dsi_parse_dt()). If the port shall
> be ignored, then reg==-1 should be passed.

All this is about purity, DECON bindings says explicitly that there
should be a port with reg=0.
So your patch and DTC warnings are incorrect from bindings PoV.
On the other side graph bindings are too bloated ( so many lines to
describe one connection ) so I am happy if there are shrinking attempts :)
Functionally nothing changes, of graph helpers assume reg=0 if it is not
present in port/endpoint node.

And regarding real issues, DECON could have more ports, possible candidates:
- GSCALER0/1/2,
- GSD/DSD - interconnect between GSCALERs and DECONs,
- SMIES - image enhancer (not implemented),
- MIC0/1 - image enhancers,
- DSIM0/1 - DSI encoders,
- HDMI - HDMI encoder.

But since all these connections can be configured dynamically, and more
importantly are inside specific SoC I dont think they need of_graphs. In
fact I think current of graph is also not necessary, but this is
different story, removal is on my long TODO list :)

Regards
Andrzej

>
> Best regards,
> Krzysztof
>
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