linux-kernel - Re: [PATCH 1/2] slimbus: ngd: dt-bindings: Add slim ngd dt bindings

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Message-ID: <9bf83e8b-df06-ead9-1075-8b1a387d6052@linaro.org>
Date:   Wed, 23 May 2018 21:01:43 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Karthikeyan Ramasubramanian <kramasub@...eaurora.org>,
        sdharia@...cinc.com, girishm@...cinc.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Banajit Goswami <bgoswami@...eaurora.org>,
        devicetree@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux-ALSA <alsa-devel@...a-project.org>
Subject: Re: [PATCH 1/2] slimbus: ngd: dt-bindings: Add slim ngd dt bindings



On 23/05/18 20:28, Rob Herring wrote:
> On Wed, May 23, 2018 at 1:11 PM, Srinivas Kandagatla
> <srinivas.kandagatla@...aro.org> wrote:
>>
>>
>> On 23/05/18 17:40, Rob Herring wrote:
>>>>
>>>> +
>>>> +- qcom,ngd-id
>>>> +       Usage: required
>>>> +       Value type: <u32>
>>>> +       Definition: ngd instance id in the controller
>>>
>>> Why do you need this?
>>>
>> Please ignore my comment from previous reply.
>>
>> There are more than one instances of ngd in this slim controller.
>> We need this to make sure we are programming the correct one.
> 
> Doesn't the parent-child relationship of devices on the bus provide
> that? 
Thanks for the hint, that sounds like the actual problem here,
If I represent the node with proper parent-child relationship like this, 
it will remove the need of this property and would work perfectly in 
case we want to support multiple ngds in future!

slim@...0000 {
	compatible = "qcom,msm8996-slim";
	reg = <0x91c0000 0x2C000>;
	interrupts = <0 163 0>;
	dmas = <&slimbam 3>, <&slimbam 4>;
	dma-names = "rx", "tx";
	#address-cells = <1>;
	#size-cells = <1>;
	ngd@1 {
		reg  = <1>;
		#address-cells = <1>;
		#size-cells = <1>;
		codec@1 {
			compatible = "slim217,1a0";
			reg  = <1 0>;
		};	
	};
};



If you mean to provide consistent numbering to userspace, then
> that's not a DT problem (nor one that Linux plans to solve).
> 
No, this is not problem am trying to solve.

>> We also need this instance ID during powering it up using QMI.
> 
> Wouldn't that be a QMI ID?

It is passed as parameter to SLIMBUS_QMI_SELECT_INSTANCE_REQ_V01 request.

thanks,
srini
> 
> Rob
>