linux-kernel - Re: [PATCHv4 8/9] ASoC: fsl-asoc-card: add DT property "cpu-system-clock-direction-out"

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Message-ID: <1607626951.349332.1715936738428.JavaMail.zimbra@savoirfairelinux.com>
Date: Fri, 17 May 2024 05:05:38 -0400 (EDT)
From: Elinor Montmasson <elinor.montmasson@...oirfairelinux.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>, 
	shengjiu wang <shengjiu.wang@...il.com>, 
	Xiubo Lee <Xiubo.Lee@...il.com>, Fabio Estevam <festevam@...il.com>, 
	Nicolin Chen <nicoleotsuka@...il.com>, 
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, 
	linux-sound <linux-sound@...r.kernel.org>, 
	devicetree <devicetree@...r.kernel.org>, 
	linux-kernel <linux-kernel@...r.kernel.org>, 
	alsa-devel <alsa-devel@...a-project.org>, 
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCHv4 8/9] ASoC: fsl-asoc-card: add DT property
 "cpu-system-clock-direction-out"

From: "Mark Brown" <broonie@...nel.org>
Sent: Thursday, 16 May, 2024 14:18:00
> On Wed, May 15, 2024 at 03:54:10PM +0200, Elinor Montmasson wrote:
>> Add new optional DT property "cpu-system-clock-direction-out" to set
>> sysclk direction as "out" for the CPU DAI when using the generic codec.
>> It is set for both Tx and Rx.
>> If not set, the direction is "in".
>> The way the direction value is used is up to the CPU DAI driver
>> implementation.
> 
> This feels like we should be using the clock bindings to specify the
> clock input of whatever is using the output from the SoC, though that's
> a lot more work.

Similarly to patch 7/9, I exposed this parameter because the driver has it, and
because there might be CPU DAIs needing this parameter.
Otherwise the cpu sysclk direction will always be IN as a default.
This parameter could be needed for cases with CPU DAIs, such as an SAI,
which can provide or consume Tx/Rx clocks.
For these devices I know the sysclk direction should correspond to
what was set in the dai format.

This new compatible is intended to be used when there is no codec
device/driver. There is technically no codec device/driver for which
the clock input can be set.

Is it a bad idea to allow setting the cpu sysclk direction only ?
Should the compatible be limited to use-cases where the cpu sysclk
direction cannot be set by the machine driver ?

Best regards,
Elinor Montmasson