linux-kernel - Re: [PATCH v1 11/15] ASoC: fsl_ssi: Setup AC97 in dai

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Date:   Thu, 4 Jan 2018 21:38:52 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     timur@...i.org, broonie@...nel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, alsa-devel@...a-project.org,
        lgirdwood@...il.com, fabio.estevam@....com, caleb@...me.org,
        arnaud.mouiche@...oxia.com, lukma@...x.de, kernel@...gutronix.de
Subject: Re: [PATCH v1 11/15] ASoC: fsl_ssi: Setup AC97 in dai_probe()

On 04.01.2018 20:07, Nicolin Chen wrote:
> On Mon, Jan 01, 2018 at 04:17:20PM +0100, Maciej S. Szmigiero wrote:
>>> AC97 configures some registers earlier to start a communication
>>> with CODECs, so this patch moves those register settings to the
>>> dai_probe() as well, along with other register configurations.
>  
>> This patch breaks AC'97 CODEC probing.
>>
>> Namely, the fsl_ssi DAI probe callback is only called after the AC'97
>> CODEC probe callback, so when you move SSI AC'97 startup to its DAI
>> probe callback it won't be done yet when the CODEC is probed (and this
>> requires a working AC'97 interface to successfully complete).
> 
> Hmm...What's the dependency here? Why is it required like this?

This patch moves enabling AC'97 communication (done by
fsl_ssi_setup_ac97() ) from SSI _platform device_ probe path to
SSI _DAI_ probe path.

However, it turns out that a SSI _DAI_ probe happens after a AC'97
CODEC probe (that is, ac97_soc_probe() in sound/soc/codecs/ac97.c).
And a AC'97 CODEC probe needs AC'97 communication to be working,
since it has to detect the CODEC model, configure it, etc.

> I am okay to put everything to a separate fsl_ssi_hw_init() and
> move it back to the platform probe() though.
> 

This could be a solution - I assume that by "everything" in the above
sentence you mean (at least) enabling the AC'97 communication at the
SSI.

Maciej