RE: Request for help: How to upgrade a sound driver from kernel 4.14 to 6.6

Thanks for the direction.

Can you suggest a resource for writing such a driver? I cannot find anything that describes what a driver would do exactly. Is there a template or example that you can suggest that I use as a starting point?

-steve

-----Original Message----- From: Lars-Peter Clausen lars@metafoo.de Sent: Saturday, May 31, 2025 11:33 PM To: Steve Broshar steve@palmerwirelessmedtech.com; alsa-devel@alsa-project.org Subject: Re: Request for help: How to upgrade a sound driver from kernel 4.14 to 6.6

Hi,

This seems to be one of the cases where chatgpt doesn't get it quite right and just makes stuff up.

Generally you still need a simple driver for you codec that at least specifies which formats and rates are supported. But this can be a really simple driver, doesn't have to do anything other than registering the codec.

On 5/30/25 14:47, Steve Broshar wrote:

Thanks for the help. I learned that to output I2S to a slave device, I shouldn't need a device-specific driver; that built-in drivers are all I need. I thought that was going to be easy to setup, but I have no luck with it. The boot log contains: platform sound-auditon: deferred probe pending

I have been working with chatgpt extensively as it seems you do too. It has a deep understanding of the linux kernel codebase. But, so far I cannot get the device to initialize (probe). Do you agree that I should be able to avoid the use of a device-specific driver? Do you see any issues in the device tree below?

Here's the device tree setup:

&sai2 { #sound-dai-cells = <0>; pinctrl-names = "default"; pinctrl-0 = <&pinctrl_sai2>; assigned-clocks = <&clk IMX8MN_CLK_SAI2>; assigned-clock-parents = <&clk IMX8MN_AUDIO_PLL1_OUT>; assigned-clock-rates = <24576000>; fsl,sai-mclk-direction-output; status = "okay"; };

pinctrl_sai2: sai2grp { fsl,pins = < MX8MN_IOMUXC_SAI2_TXC_SAI2_TX_BCLK 0xd6 MX8MN_IOMUXC_SAI2_TXFS_SAI2_TX_SYNC 0xd6 MX8MN_IOMUXC_SAI2_TXD0_SAI2_TX_DATA0 0xd6 //MX8MN_IOMUXC_SAI2_RXD0_SAI2_RX_DATA0 0xd6 MX8MN_IOMUXC_SAI2_MCLK_SAI2_MCLK 0xd6 >; };

// Compton audio output does not require a device-specific codec; the built-in, dummy driver is sufficient codec_auditon: codec-snd-doc-dummy { compatible = "linux,snd-soc-dummy"; #sound-dai-cells = <0>; };

// audio output for Compton can be accomplished via the built-in simple-audio-card driver // since only need to stream I2S; device (ADAU1467) does not require setup/control sound-auditon { // specify the built-in simple sound card driver compatible = "simple-audio-card"; // description that shows in userland; i.e. via 'aplay -l' // auditon: a quantum of sound ;) simple-audio-card,name = "auditon"; // specify stream format // supported options: i2s, right_j, left_j, dsp_a, dsp_b, ac97, pdm, msb, lsb //simple-audio-card,format = "i2s"; // with i2s, boot log shows: deferred probe pending and no device is setup simple-audio-card,format = "dsp_a"; // assign CPU as master for bit-clock simple-audio-card,bitclock-master = <&cpu_link_auditon>; // assign CPU as master for frame-clock simple-audio-card,frame-master = <&cpu_link_auditon>;

status = "okay";

cpu_link_auditon: simple-audio-card,cpu {
	sound-dai = <&sai2>;
	dai-tdm-slot-num = <2>; // 2=>stereo
	dai-tdm-slot-width = <32>; // bits per slot
};

simple-audio-card,codec {
	sound-dai = <&codec_auditon>;
};

};

Thanks in advance.

Steve Broshar Palmer Wireless Medtech