Re: [PATCH v2] drm/exynos: Get HDMI version from device tree

[Rahul Sharma <r.sh.open@gmail.com>]

On Thu, Jan 31, 2013 at 10:22 AM, Inki Dae <inki.dae@samsung.com> wrote:
> 2013/1/31 Stephen Warren <swarren@wwwdotorg.org>:
>> On 01/30/2013 06:16 PM, Inki Dae wrote:
>>> 2013/1/30 Sylwester Nawrocki <sylvester.nawrocki@gmail.com>:
>>>> Hi,
>>>>
>>>>
>>>> On 01/08/2013 11:56 PM, Stephen Warren wrote:
>>>>>
>>>>> On 01/08/2013 01:16 PM, Sean Paul wrote:
>>>>>>
>>>>>> Add a property to the hdmi node so we can specify the HDMI version in
>>>>>> the device tree instead of just defaulting to v1.4 with the existence of
>>>>>> the dt node.
>>>>>
>>>>>
>>>>> I guess this seems OK to me if required, although I'd certainly like to
>>>>> see someone familiar with the Exynos HW confirm whether this should be
>>>>> driven purely by DT compatible value for the HDMI IP block instead though.
>>>>
>>>>
>>>> I think the supported HDMI standard is something that could well be derived
>>>> from the compatible property. The IP supporting v1.3 and v1.4 will be
>>>> significantly different, so this would anyway already need to be reflected
>>>> in the compatible property. The only issue I see here is that people tend
>>>> to make the compatible string overly generic, so it is hardly usable for
>>>> anything but matching an IP with its driver. For instance for exynos5 we
>>>> have now (Documentation/devicetree/bindings/drm/exynos/hdmi.txt):
>>>>
>>>>         compatible = "samsung,exynos5-hdmi";
>>>>
>>>> For Exynos4 series there were already some patches proposed [1], but I
>>>> believe
>>>> this isn't a clean solution. Instead of things like:
>>>>
>>>> compatible = "samsung,exynos4-hdmi13";
>>>> compatible = "samsung,exynos4-hdmi14";
>>>>
>>>> I would much more like to see the SoC version embedded in the compatible
>>>> string, e.g.
>>>>
>>>
>>> Hi Sylwester. long time no see.
>>>
>>> I think that if we use the SoC version embedded in the compatible
>>> string then each driver shoud aware of the ip version to the SoC to
>>
>> The driver only needs to be aware of one SoC version for each IP version.
>>
>
> I know that device tree describes hw information and the information
> includes ip version also. So shouldn't the driver aware of the ip
> version itself and should the driver only aware of it through device
> tree? So I thought using the version property is proper way.
>

I want to second Sylwester's proposal. Compatibility information
should be carried in compatible string. 'version' property is diluting
its purpose. With this implementation, all compatible strings :
"exynos-hdmi", "exynos4-hdmi", "exynos4x12-hdmi",
"exynos5-hdmi" ... have same relevance.

IMO, it make sense with compatible strings specifying the
first Soc with same IP version:
compatible = "samsung,exynos4210-hdmi";
compatible = "samsung,exynos4212-hdmi";

compatible = "samsung,exynos-hdmi-1.3" and
compatible = "samsung,exynos-hdmi-1.4" will also do the needful.

While representing hdmi version information we should consider
the possibility of intermediate releases like 1.3ab, 1.4a etc.

regards,
Rahul Sharma.

>
>> So with Sylwester's proposal:
>>
>>>> compatible = "samsung,exynos4210-hdmi"; /* among others it carries an
>>>>                                           information this IP supports
>>>>                                           HDMI v1.3 */
>>>>
>>>> compatible = "samsung,exynos4212-hdmi"; /* HDMI v1.4, IIRC */
>>
>> The driver woulud only ever have to know about those two compatible
>> values (unless further incompatible HW revisions exist); any other SoC
>> would be listed as being compatible with one of those two strings (but
>> in addition to the specific value for the specific SoC, e.g. compatible
>> = "samsung,exynox5xxx-hdmi", "samsung,exynos4212-hdmi").
>>
>>> use version specific feature so I think it's better to use it without
>>> the SoC version embedded in the compatible string like this,
>>> compatible = "samsung,exynos4-hdmi"
>>> version = "0x104" or "0x103"
>>
>> That would be quite non-typical.
>>
>>> With this, all each driver to do  is to check version property and set
>>> version specific feature properly. And we have some dtsi file to can
>>> be used commonly.
>>>
>>> For example,
>>> exynos4.dtsi : have all Exynos4 series SoCs common properties and also
>>> use common compatible string.
>>> exynos4412.dtsi, exynos4212.dtsi and so on: have Exynos42xx specific
>>> properties. So the hdmi version string could be used here as "version
>>> = "0x104" or "0x103"
>>> exynos4412-board.dts: have board specific properties.
>>>
>>> compatible = "samsung,exynos5-hdmi" is reasonable to me.
>>> any opinions?
>>
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