SPDIFRX Linux driver

Applicable for

STM32MP13x lines, STM32MP15x lines, STM32MP21x lines, STM32MP23x lines, STM32MP25x lines

---

1. Article purpose

This article introduces the SPDIFRX Linux^® driver for the SPDIFRX internal peripheral.

2. Short Description

The SPDIFRX Linux driver is an ASoC CPU DAI driver implemented in the Linux ALSA framework.

3. Configuration

3.1. Kernel Configuration

Activate the SPDIFRX Linux driver in the kernel configuration using the Linux Menuconfig tool: Menuconfig or how to configure kernel

[*] Device Drivers
    [*] Sound card support
        [*] Advanced Linux Sound Architecture
            [*] ALSA for SoC audio support
                STMicroelectronics STM32 SOC audio support
	             [*] STM32 S/PDIF receiver (SPDIFRX) support

3.2. Device tree

Refer to the SPDIFRX device tree configuration article when configuring the SPDIFRX Linux kernel driver.

4. How to use

The SPDIFRX driver is accessed from userland through an ALSA device. Refer to ALSA overview to see how to list and use ALSA devices.

The SPDFIRX driver exposes an alsa control, which allows to retrieve the IEC958 status bits from the input audio stream.

Warning

The configuration of the SPDIFRX input pin in the device tree, may put some restrictions on the use of IEC958 control. Thus, in some configuration, the control can be used only when an audio stream is captured. Refer to the SPDIFRX device tree configuration article, to find details about SPDIFRX configuration.

5. How to debug

The debugfs and procfs file systems can be checked to get information about the SPDFIRX driver and the resources it uses. A none exhaustive list of these file system entries is provided below. Refer to ALSA overview to get more details about debugging tools.

• debugfs entries:

• asoc: refer to ALSA_overview#How_to_monitor
• clk: refer to Clock_overview#How_to_monitor_with_debugfs_of_clock_framework to get information on clocks.
• pinctrl: refer to Pinctrl_overview#How_to_monitor to get information on pins.
• regmap: allow to monitor SPDIFRX peripheral registers.

$ cat /sys/kernel/debug/regmap/xxx.audio-controller/registers

• procfs entries:

• asound: refer to ALSA_overview#How_to_debug
• interrupts: allow to check interrupts.

$ cat /proc/interrupts

6. Source code location

sound/soc/stm/stm32_spdifrx.c : implements the SPDIFRX driver.