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Message-ID: <13faa6c8-ad4f-4f81-935a-5ea74621d373@bootlin.com>
Date: Fri, 15 Mar 2024 15:45:24 +0100
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Subject: Re: [PATCH 09/13] ASoC: ti: davinci-i2s: Enable unexpected frame
 pulses detection
To: Mark Brown <broonie@kernel.org>
Cc: Liam Girdwood <lgirdwood@gmail.com>, Rob Herring <robh+dt@kernel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
 Conor Dooley <conor+dt@kernel.org>, Peter Ujfalusi
 <peter.ujfalusi@gmail.com>, Jaroslav Kysela <perex@perex.cz>,
 Takashi Iwai <tiwai@suse.com>, linux-sound@vger.kernel.org,
 devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
 alsa-devel@alsa-project.org, Thomas Petazzoni
 <thomas.petazzoni@bootlin.com>, herve.codina@bootlin.com,
 christophercordahi@nanometrics.ca
References: <20240315112745.63230-1-bastien.curutchet@bootlin.com>
 <20240315112745.63230-10-bastien.curutchet@bootlin.com>
 <51866f62-460d-4035-bcf1-b9f03cf9be0b@sirena.org.uk>
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From: Bastien Curutchet <bastien.curutchet@bootlin.com>
In-Reply-To: <51866f62-460d-4035-bcf1-b9f03cf9be0b@sirena.org.uk>
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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