linux-kernel - Re: [PATCH v3 06/14] Documentation: drm/bridge: add document for analogix

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Message-id: <55DBC657.6060409@samsung.com>
Date:	Tue, 25 Aug 2015 10:35:19 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Yakir Yang <ykk@...k-chips.com>,
	Rob Herring <robherring2@...il.com>
Cc:	heiko@...ech.de, Sean Paul <seanpaul@...gle.com>,
	Takashi Iwai <tiwai@...e.de>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Andrzej Hajda <a.hajda@...sung.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Vincent Palatin <vpalatin@...omium.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	linux-rockchip@...ts.infradead.org,
	Russell King <rmk+kernel@....linux.org.uk>,
	Thierry Reding <treding@...dia.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	David Airlie <airlied@...ux.ie>,
	Doug Anderson <dianders@...gle.com>,
	Inki Dae <inki.dae@...sung.com>,
	Ajay kumar <ajaynumb@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mark Yao <mark.yao@...k-chips.com>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Jingoo Han <jingoohan1@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Daniel Kurtz <djkurtz@...gle.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Kumar Gala <galak@...eaurora.org>,
	Joe Perches <joe@...ches.com>,
	Andy Yan <andy.yan@...k-chips.com>
Subject: Re: [PATCH v3 06/14] Documentation: drm/bridge: add document for
 analogix_dp

On 25.08.2015 10:33, Yakir Yang wrote:
> Hi Krzysztof,
> 
> 在 2015/8/25 7:49, Krzysztof Kozlowski 写道:
>> On 24.08.2015 21:48, Yakir Yang wrote:
>>> Hi Krzysztof,
>>>
>>> 在 08/24/2015 12:20 PM, Krzysztof Kozlowski 写道:
>>>> On 24.08.2015 11:42, Yakir Yang wrote:
>>>>> Hi Krzysztof,
>>>>>
>>>>> 在 08/23/2015 07:43 PM, Krzysztof Kozlowski 写道:
>>>>>> 2015-08-24 8:23 GMT+09:00 Rob Herring <robherring2@...il.com>:
>>>>>>> On Wed, Aug 19, 2015 at 9:50 AM, Yakir Yang <ykk@...k-chips.com>
>>>>>>> wrote:
>>>>>>>> Analogix dp driver is split from exynos dp driver, so we just
>>>>>>>> make an copy of exynos_dp.txt, and then simplify exynos_dp.txt
>>>>>>>>
>>>>>>>> Beside update some exynos dtsi file with the latest change
>>>>>>>> according to the devicetree binding documents.
>>>>>>> You can't just change the exynos bindings and break
>>>>>>> compatibility. Is
>>>>>>> there some agreement with exynos folks to do this?
>>>>>> No, there is no agreement. This wasn't even sent to Exynos
>>>>>> maintainers.
>>>>> Sorry about this one, actually I have add Exynos maintainers in
>>>>> version
>>>>> 1 & version 2,
>>>>> but lose some maintainers in version 3, I would fix it in bellow
>>>>> versions.
>>>>>
>>>>>> Additionally the patchset did not look interesting to me because of
>>>>>> misleading subject - Documentation instead of "ARM: dts:".
>>>>>>
>>>>>> Yakir, please:
>>>>>> 1. Provide backward compatibility. Mark old properties as deprecated
>>>>>> but still support them.
>>>>> Do you mean that I should keep the old properties declare in
>>>>> exynos-dp.txt,
>>>>> but just mark them as deprecated flag.
>>>> That is one of ways how to do this. However more important is that
>>>> driver should still support old bindings so such code:
>>>> -       if (of_property_read_u32(dp_node, "samsung,color-space",
>>>> +       if (of_property_read_u32(dp_node, "analogix,color-space",
>>>>
>>>> is probably wrong. Will the driver support old DTB in the same way
>>>> as it
>>>> was supporting before the change?
>>> Okay, I got your means. So document is not the focus, the most important
>>> is that
>>> driver should support the old dts prop.
>> Right, the focus is on the driver.
>>
>>> If so the new analogix dp driver
>>> should keep
>>> the "samsung,color-space", rather then just mark it with [DEPRECATED]
>>> flag.
>> If you are replacing a binding/property then it should be marked
>> deprecated. This means that the old property is still working but new
>> users of it should not be added.
> 
> Okay, so just quote Heiko's reply, such code would be need in analogix
> dp driver.
> 
>        if (of_property_read_u32(dp_node, "analogix,color-space",
>                                  &dp_video_config->color_space))
>            if (of_property_read_u32(dp_node, "samsung,color-space",
>                                      &dp_video_config->color_space)) {
> 
>                     dev_err(dev, "failed to get color-space\n");
>                     return ERR_PTR(-EINVAL);
>             }

Yes. It does not look pretty but something like this is needed.

Best regards,
Krzysztof

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