linux-kernel - Re: [alsa-devel] [PATCH 10/10] ASoC: Add codec component for AD242x nodes

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Message-ID: <ff0e2420-a2c6-17e7-2761-f6544e2c0cb7@linux.intel.com>
Date:   Wed, 18 Dec 2019 09:32:40 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Daniel Mack <daniel@...que.org>, linux-kernel@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org,
        alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org
Cc:     lars@...afoo.de, sboyd@...nel.org, mturquette@...libre.com,
        robh+dt@...nel.org, broonie@...nel.org, pascal.huerst@...il.com,
        lee.jones@...aro.org
Subject: Re: [alsa-devel] [PATCH 10/10] ASoC: Add codec component for AD242x
 nodes



On 12/18/19 3:49 AM, Daniel Mack wrote:
> Hi,
> 
> On 12/17/19 8:28 PM, Pierre-Louis Bossart wrote:
>> On 12/9/19 12:35 PM, Daniel Mack wrote:
> 
>>> +    if (!ad242x_node_is_master(priv->node) &&
>>> +       ((format & SND_SOC_DAIFMT_MASTER_MASK) !=
>>> SND_SOC_DAIFMT_CBM_CFM)) {
>>> +        dev_err(component->dev, "slave node must be clock master\n");
>>> +        return -EINVAL;
>>> +    }
>>
>> It was my understanding that the master node provides the clock to the
>> bus, so not sure how it could be a clock slave, and conversely how a
>> slave node could provide a clock to the bus?
> 
> The slave nodes receive the A2B clock from the master node and then
> produce digital audio output that is sent to other components such as
> codecs. Hence, in ASoC terms, they are the clock master.
> 
> Likewise, as the master node is receiving its clock from other
> components, it has to be a clock slave in the audio network.
> 
> Does that make sense?

Your slave node acts as a bridge then, but it seems you don't model the 
bus-facing interface, which has to follow the master clock. Or do you?

Likewise the master has an 'SOC-facing' interface and a bus-facing 
interface. it *could* be master on both if ASRC was supported. The point 
is that the bus-facing interface is not clock slave.