linux-kernel - Re: [PATCH 12/13] ASoC: dt-bindings: davinic-mcbsp: Add the 'ti,drive-dx' property

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Date: Wed, 20 Mar 2024 08:46:20 +0100
From: Bastien Curutchet <bastien.curutchet@...tlin.com>
To: Péter Ujfalusi <peter.ujfalusi@...il.com>,
 Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
 Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
 Takashi Iwai <tiwai@...e.com>
Cc: 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 12/13] ASoC: dt-bindings: davinic-mcbsp: Add the
 'ti,drive-dx' property

Hi Péter,


On 3/19/24 19:02, Péter Ujfalusi wrote:
> 
> 
> On 15/03/2024 13:27, Bastien Curutchet wrote:
>> McBSP is able to handle capture and playback stream.
>> The McBSP's DX pins that outputs serial data during playback streams can
>> be used to output a chosen pattern during capture streams. For instance,
>> this can be useful to drive an active-low signal during capture streams
>> (by choosing <0> as pattern)
> 
> or configure the MCBSPx.DX pin as GPO and use it as a GPIO?

In my use case, DX pin is connected to the ADC chip select pin so I want
the DX pin to toggle the closest possible to capture's start. That's
why I introduced this feature over configuring the pin as GPO.

> 
> Quite novel use of the hardware, no doubt about it. If you don't have
> DMA servicing the TX, it will just re-transmit the word from from the
> DXR register when the transmitter is pulled out of reset.
> 
> Interesting, but I'm not sure if this belongs to DT.
> 
>> Add a 'ti,drive-dx' property that can be used to repeatedly output a
>> chosen pattern on DX pin while capture stream is ON.
>>
>> Signed-off-by: Bastien Curutchet <bastien.curutchet@...tlin.com>
>> ---
>>   Documentation/devicetree/bindings/sound/davinci-mcbsp.yaml | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/sound/davinci-mcbsp.yaml b/Documentation/devicetree/bindings/sound/davinci-mcbsp.yaml
>> index d8d4e7ea6e02..f4d1fc6bcd61 100644
>> --- a/Documentation/devicetree/bindings/sound/davinci-mcbsp.yaml
>> +++ b/Documentation/devicetree/bindings/sound/davinci-mcbsp.yaml
>> @@ -80,6 +80,13 @@ properties:
>>         Enable synchronisation error detections when an unexpected frame pulse is
>>         received. If not present, unexpected frame pulses are ignored.
>>   
>> +  ti,drive-dx:
>> +    $ref: /schemas/types.yaml#/definitions/uint32
>> +    description:
>> +      If the property is present, McBSP will repeatedly output the selected
>> +      value on DX pin during capture streams. For instance, if set to 0, this
>> +      can be used to drive an active-low signal.
>> +
>>   required:
>>     - "#sound-dai-cells"
>>     - compatible
> 

Best regards,
Bastien