Kernel Compatibility

The aes-stream-drivers codebase targets Linux kernels from 3.10 through the current 6.8+ series. This range spans major kernel API changes: the /proc interface was restructured, DMA mapping APIs evolved, and several subsystem function signatures changed across that period. Rather than requiring a specific kernel version, the driver uses LINUX_VERSION_CODE compile-time guards to select the correct API call for each kernel generation.

How the Guards Work

The standard Linux kernel macros LINUX_VERSION_CODE and KERNEL_VERSION(major, minor, patch) are used throughout the common driver source. A typical guard looks like:

#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 6, 0)
    /* use old file_operations.proc_fops pattern */
#else
    /* use proc_ops struct (introduced in 5.6) */
#endif

No custom abstraction layer wraps these guards. Each guard is local to the file and function where the API difference appears.

Compatibility Matrix

The following guards are present in the driver source. All were verified by direct inspection of the source files listed.

< KERNEL_VERSION(2, 6, 25) — dma_common.c

ioremap_nocache is used in place of ioremap for non-cacheable register mapping. The nocache variant was removed in 2.6.25.

< KERNEL_VERSION(3, 10, 0) — dma_common.c

Old /proc API: PDE(inode)->data is used to retrieve the private pointer from a /proc inode. This was replaced by PDE_DATA() in 3.10.

< KERNEL_VERSION(4, 16, 0) — dma_common.h

The __poll_t type did not exist before 4.16. The driver provides a manual typedef unsigned int __poll_t for older kernels.

< KERNEL_VERSION(5, 6, 0) — dma_common.c

The proc_ops struct was introduced in 5.6 to replace embedding function pointers directly in file_operations for /proc entries.

< KERNEL_VERSION(5, 15, 0) — dma_buffer.c

DMA mapping API changes in 5.15 affected how streaming DMA buffers are managed.

>= KERNEL_VERSION(5, 15, 0) — rce_top.c

An RCE-specific compatibility change for the same DMA API evolution.

>= KERNEL_VERSION(5, 17, 0) or RHEL 9.3 — dma_common.c

pde_data() (lowercase) replaces the older PDE_DATA() macro. Red Hat backported this change into RHEL 9.3 with an older kernel version number, requiring explicit RHEL_RELEASE_CODE detection.

>= KERNEL_VERSION(6, 0, 0) — Yocto axistreamdma.c

Coherent DMA memory allocation is configured via the device tree dma-coherent attribute instead of a build-time define.

>= KERNEL_VERSION(6, 4, 0) or RHEL 9.4 — dma_common.c, aximemorymap

class_create() dropped its first argument (THIS_MODULE) in 6.4. Red Hat backported this change in RHEL 9.4.

RHEL Backport Detection

Red Hat Enterprise Linux backports upstream API changes into kernel versions whose LINUX_VERSION_CODE predates the upstream introduction. For example, RHEL 9.3 ships with a 5.14.x-based kernel but includes the pde_data() change from upstream 5.17. The driver detects this using the RHEL_RELEASE_CODE macro alongside LINUX_VERSION_CODE guards.

This means the driver’s compatibility range is not simply “kernels 3.10–6.8” but more accurately “any kernel whose symbol set matches the guards above, including RHEL backport variants.”

Minimum and Maximum Tested Kernels

The minimum supported kernel is 3.10 — this is the version that introduced the PDE_DATA() macro used in the /proc interface code. Kernels older than 3.10 are not supported. The driver is tested in CI through kernel 6.8+ (current as of this writing). Kernels beyond 6.8 may require new guards if further API changes occur.

Further Reading