Bard Liao

A bug has been resolved in the Linux kernel related to a null dereference on system suspend entry. When the system enters suspend with an active stream, the SOF core calls `hw params upon resume()`. On Intel platforms with HDA DMA used to manage the link DMA, this leads to a call chain of `hda dsp set hw params upon resume()` -> `hda dsp dais suspend()` -> `hda dai suspend()` -> `hda ipc4 post trigger()`. A bug is hit in `hda dai suspend()` as `hda link dma cleanup()` is run first, which clears `hext stream->link substream`, and then `hda ipc4 post trigger()` is called with a NULL `snd pcm substream` pointer.

The issue occurs when the system is suspended while audio is active, causing the `sof ipc4 pcm hw free()` function to reset the pipelines. If the firmware crashes during audio playback or when resetting the stream before suspend, the `sof ipc4 set multi pipeline state()` function will fail with an IPC error, interrupting the state change. This misalignment between the kernel and firmware state can result in errors returned by firmware for IPC messages, eventually failing the audio resume. The kernel state will be corrected on the next DSP boot after the DSP panic.