linux-kernel - Re: [PATCH 09/13] ASoC: ti: davinci-i2s: Enable unexpected frame pulses detection

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Date: Fri, 15 Mar 2024 15:45:24 +0100
From: Bastien Curutchet <bastien.curutchet@...tlin.com>
To: Mark Brown <broonie@...nel.org>
Cc: Liam Girdwood <lgirdwood@...il.com>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Peter Ujfalusi
 <peter.ujfalusi@...il.com>, Jaroslav Kysela <perex@...ex.cz>,
 Takashi Iwai <tiwai@...e.com>, linux-sound@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 alsa-devel@...a-project.org, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, herve.codina@...tlin.com,
 christophercordahi@...ometrics.ca
Subject: Re: [PATCH 09/13] ASoC: ti: davinci-i2s: Enable unexpected frame
 pulses detection

Hi Mark,

On 3/15/24 15:09, Mark Brown wrote:
> On Fri, Mar 15, 2024 at 12:27:41PM +0100, Bastien Curutchet wrote:
> 
>> McBSP can generate an SYNCERR when unexpected frame pulses are
>> detected. The driver always disables this feature and ignore the
>> unexpected frame pulses.
> 
> What does "unexpected" mean?

Unexpected frame sync pulse is defined in datasheet as a sync pulse that 
occurs <N> bit clocks earlier than the last transmitted bit of the 
previous frame. The <N> can be configured through registers.

> 
>> Enable the generation of SYNCERR by the McBSP according to the
>> 'ti,enable-sync-err' device-tree property.
> 
> Why would this be optional, and how is this reported - I'm not seeing
> any interrupt handling updates?

It is possible to deliberately ignore them and that is what is done 
today in the driver.
This is reported as a status bit in a register. An interrupt can indeed 
be generated from this but I'm not using it (now at least).
I use the fact that McBSP automatically drops previous element and 
starts a new reception when an unexpected frame pulse occurs.

Best regards,
Bastien