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Subject: Re: [PATCH 1/4] ARM: dts: exynos5250: Add #sound-dai-cells property
 to hdmi device node
To:     Inki Dae <inki.dae@samsung.com>, krzk@kernel.org
Cc:     kgene@kernel.org, devicetree@vger.kernel.org,
        linux-samsung-soc@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        b.zolnierkie@samsung.com, m.szyprowski@samsung.com
From:   Sylwester Nawrocki <s.nawrocki@samsung.com>
Message-id: <39965bce-a6f2-6202-5c3f-97e4446e97eb@samsung.com>
Date:   Fri, 09 Mar 2018 12:52:58 +0100
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Hi Inki,

On 03/09/2018 03:40 AM, Inki Dae wrote:
> 2018년 03월 08일 02:27에 Sylwester Nawrocki 이(가) 쓴 글:
>> This property is required for specifying link between the HDMI IP block
>> and the SoC's audio subsystem.
>>
>> Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
>> ---
>>  arch/arm/boot/dts/exynos5250.dtsi | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/arm/boot/dts/exynos5250.dtsi b/arch/arm/boot/dts/exynos5250.dtsi
>> index 56626d1a4235..71d2ede118e3 100644
>> --- a/arch/arm/boot/dts/exynos5250.dtsi
>> +++ b/arch/arm/boot/dts/exynos5250.dtsi
>> @@ -700,6 +700,7 @@
>>  					"sclk_hdmiphy", "mout_hdmi";
>>  			samsung,syscon-phandle = <&pmu_system_controller>;
>>  			phy = <&hdmiphy>;
>> +			#sound-dai-cells = <0>;
> 
> This patch adds this property to hdmi device node which is bound by HDMI driver 
> of Exynos DRM. As we talked about this at other email thread, seems this property 
> is required mandatorily for Odroid XU3/4 board which uses Exynos5422.
> There may be something I'm missing so could you let me know how this property 
> is required?

It is required to properly interpret the list of DAI specified in the 'sound-dai'
property. If a device supports only one DAI it will have #sound-dai-cells = <0>
and the sound-dai property values in cpu<->codec link may look like this:

 cpu { ... }
 codec {
	 sound-dai = <&max98090>, <&hdmi>;
 };

When the CODEC support more DAIs it will have #sound-dai-cells = <1> and we can
additionally specify which DAI we exactly refer to, in this case DAI 0:

 cpu { ... }
 codec {
	sound-dai = <&max98095 0>, <&hdmi>;
 };

More details can be found in documentation of of_parse_phandle_with_args()
function.

The above refers to cpu/codec mapping like I2S0 -> [max9809x, hdmi], on Exynos5433
we have I2S0 -> wm5110 and I2S1 -> hdmi.


-- 
Regards,
Sylwester