linux-kernel - Re: [PATCH v4 5/6] arm64: dts: imx8mp: Add fsl,dsp-ctrl property for dsp

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Message-ID: <da63fc79-76f6-443f-b1fe-c4242cb45328@gmail.com>
Date: Wed, 12 Feb 2025 21:04:47 +0200
From: Laurentiu Mihalcea <laurentiumihalcea111@...il.com>
To: Frank Li <Frank.li@....com>, Daniel Baluta <daniel.baluta@....com>
Cc: shawnguo@...nel.org, robh@...nel.org, s.hauer@...gutronix.de,
 kernel@...gutronix.de, krzk+dt@...nel.org, conor+dt@...nel.org,
 festevam@...il.com, devicetree@...r.kernel.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 aisheng.dong@....com, daniel.baluta@...il.com, laurentiu.mihalcea@....com,
 shengjiu.wang@....com, iuliana.prodan@....com, a.fatoum@...gutronix.de,
 Peng Fan <peng.fan@....com>
Subject: Re: [PATCH v4 5/6] arm64: dts: imx8mp: Add fsl,dsp-ctrl property for
 dsp

On 2/12/2025 6:02 PM, Frank Li wrote:
> On Wed, Feb 12, 2025 at 10:52:21AM +0200, Daniel Baluta wrote:
>> Audio block control contains a set of registers and some of them used for
>> DSP configuration.
>>
>> Drivers (rproc, SOF) are using fsl,dsp-ctrl property in order to control
>> the DSP, particularly for Run/Stall bit.
>>
>> Note that audio block control doesn't offer the functionality to reset
>> thte DSP. Reset is done via DAP interface.
>>
>> Reviewed-by: Iuliana Prodan <iuliana.prodan@....com>
>> Reviewed-by: Peng Fan <peng.fan@....com>
>> Signed-off-by: Daniel Baluta <daniel.baluta@....com>
>> ---
>>  arch/arm64/boot/dts/freescale/imx8mp.dtsi | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/boot/dts/freescale/imx8mp.dtsi b/arch/arm64/boot/dts/freescale/imx8mp.dtsi
>> index 14cfbd228b45..46b33fbb9bd1 100644
>> --- a/arch/arm64/boot/dts/freescale/imx8mp.dtsi
>> +++ b/arch/arm64/boot/dts/freescale/imx8mp.dtsi
>> @@ -1609,7 +1609,7 @@ sdma2: dma-controller@...10000 {
>>  			};
>>
>>  			audio_blk_ctrl: clock-controller@...20000 {
>> -				compatible = "fsl,imx8mp-audio-blk-ctrl";
>> +				compatible = "fsl,imx8mp-audio-blk-ctrl", "syscon";
>>  				reg = <0x30e20000 0x10000>;
>>  				#clock-cells = <1>;
>>  				#reset-cells = <1>;
>> @@ -2425,6 +2425,7 @@ dsp: dsp@...e8000 {
>>  			mboxes = <&mu2 0 0>, <&mu2 1 0>, <&mu2 3 0>;
>>  			firmware-name = "imx/dsp/hifi4.bin";
>>  			memory-region = <&dsp_reserved>;
>> +			fsl,dsp-ctrl = <&audio_blk_ctrl>;
> I think kk's comments in v3
>
> "This should have been implemented as reset controller, not syscon. It's
> really poor choice to call everything syscon. It does not scale, does
> not provide you runtime PM or probe ordering (device links). Quick look
> at your drivers suggest that you have exacvtly that problems."
>
> The above is quite good suggestion.
>
> Your reply "But for Run/Stall bits we need to use a syscon.",
>
> Run/Stall actually is reset, Most system, release reset signal means dsp/core
> RUN.
>
> Frank

RESET and STALL are quite different signals w/ different purposes so
calling them both RESET is confusing and inaccurate.

The syscon is used here to control the STALL signal (name of the bit we're using is RunStall)
and has nothing to do with the RESET signal, which is why it's implemented as a syscon rather
than a reset controller.

While Krzysztof's comment does make sense, I still find it odd to have this implemented as a
reset controller despite it not having anything to do with the RESET signal.

Also, do note that the two nodes are in clock provider-consumer relationship
so unless I'm gravely mistaken this should at least guarantee the probe order.