app: kconfig: allow FLIX generation by dcpleung · Pull Request #10511 · thesofproject/sof

dcpleung · 2026-01-30T18:11:24Z

This sets the toolchain kconfig to allow generating FLIX instructions as it is disabled by default on Zephyr upstream.

dcpleung · 2026-01-30T18:12:31Z

@lgirdwood @kv2019i When updating to the latest Zephyr SHA, you will need the kconfig to restore the previous behavior of FLIX instruction generation.

softwarecki · 2026-02-02T09:51:03Z

I was misled by the Zephyrs PR title "cmake: toolchain/xt-clang: allow to skip FLIX generation". The title suggested adding an option to optionally disable FLIX generation, not changing the default behavior to disable it. The PR description explicitly states that:

FLIX generation is enabled by default. This lets the application developers to disable FLIX generation if needed.

Based on that, I expected an opt-out mechanism only, without altering the default state.

If FLIX needs to be disabled for sof application configuration, it should be done explicitly in the Linux overlay, without unnecessarily degrading performance or changing defaults for other platforms.

abonislawski · 2026-02-02T10:59:01Z

app/Kconfig


+# Allow compiler to determine whether to generate FLIX instructions.
+choice COMPILER_CODEGEN_VLIW
+        default COMPILER_CODEGEN_VLIW_AUTO if "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "xt-clang"


VLIW is a generic term which can be a project default (AUTO) state regardless of compiler, no need to specify xt-clang here

I'm pretty sure GCC cant emit VLIW for xtensa so it will need some check for Cadence compilers like above.

"AUTO" != "enabled", it means compiler will decide (use default config)

"AUTO" != "enabled", it means compiler will decide (use default config)

ok, so you are confirming no impact for GCC here and Zephyr SDK i.e. I just want to confirm we wont be passing any --enable-flix=auto type arguments to GCC which it wont understand if we remove the compiler check.

It is only a configuration option, not a value passed to the compiler command line. The "auto" value does not result in setting any compile options.
https://github.com/zephyrproject-rtos/zephyr/blob/b4108b53f6d7ca8c1da596c7130318e64e26eaf0/CMakeLists.txt#L562-L568

@dcpleung sounds like we have all got alignment now so I think good to update and make non draft ?

Separated out the west.yml change into its own commit. So should be good to go.

lgirdwood

LGTM

lgirdwood · 2026-02-02T12:56:20Z

app/Kconfig


+# Allow compiler to determine whether to generate FLIX instructions.
+choice COMPILER_CODEGEN_VLIW
+        default COMPILER_CODEGEN_VLIW_AUTO if "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "xt-clang"


I'm pretty sure GCC cant emit VLIW for xtensa so it will need some check for Cadence compilers like above.

dcpleung · 2026-02-02T18:17:29Z

The original idea was to add an option to disable it on demand. However, it turned out that FLIX was causing multiple CI failures so that needs to be disabled by default. Zephyr main should provide a stable foundation for others to build on. Hence this PR to re-enable it to keep the old behavior.

lgirdwood · 2026-02-03T13:13:10Z

The original idea was to add an option to disable it on demand. However, it turned out that FLIX was causing multiple CI failures so that needs to be disabled by default. Zephyr main should provide a stable foundation for others to build on. Hence this PR to re-enable it to keep the old behavior.

@dcpleung just to be aligned - Zephyr main will be FLIX disabled for stability ? For SOF application/module logic we need FLIX enabled for performance.

I assume we are good to disable for Zephyr and enable for SOF, i.e. there's no FLIX support needed in Zephyr for managing any ISA/registers (and I dont think there are any?) e.g. around context switches or thread scheduling ?

dcpleung · 2026-02-03T18:24:33Z

@dcpleung just to be aligned - Zephyr main will be FLIX disabled for stability ? For SOF application/module logic we need FLIX enabled for performance.

Yes. That's correct. Though you will need the kconfig changes in this PR when you move to newer Zephyr.

I assume we are good to disable for Zephyr and enable for SOF, i.e. there's no FLIX support needed in Zephyr for managing any ISA/registers (and I dont think there are any?) e.g. around context switches or thread scheduling ?

FLIX does not need any registers. It's simply fusing instructions together for density and parallel execution.

Total of 1145 commits. Changes include: a5a9ff4c28c xtensa: handle instruction TLB multi-hit exception 9b9e9ebde77 xtensa: mmu: data TLB multi-hit only handle exception address 599df95875c xtensa: return back to interrupted thread for certain exceptions 27e48026215 xtensa: remove unnecessary setting of is_fatal_error during exc 8d072e85b1e ipc: intel_adsp: fix inverted sync wait condition ed4cec2d220 xtensa: ptables: doxygen doc 744a7f4daf1 xtensa: mmu: do doxygen for functions 50e980d9a83 xtensa: mmu: halt system if not enough L2 tables during boot 82b7d94d452 xtensa: mmu: add debug logs on page table allocations 0777dbea028 xtensa: mmu: assert when L2 table allocation fails during dup 71262d0e075 arch: xtensa: avoid the use of "sanity check" term Signed-off-by: Daniel Leung <daniel.leung@intel.com>

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Pull request overview

This PR enables FLIX (Flexible Length Instruction eXtension) instruction generation for the Xtensa toolchain by updating the Zephyr revision and adding Kconfig configuration to allow the compiler to automatically determine whether to generate FLIX instructions.

Changes:

Updated Zephyr upstream revision to a newer commit
Added Kconfig choice for COMPILER_CODEGEN_VLIW to enable automatic FLIX instruction generation when using xt-clang toolchain

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
west.yml	Updates Zephyr revision to 05a3f62f4456b25f1830eeb1a09c39e4a2a8bc39 to support FLIX configuration
app/Kconfig	Adds COMPILER_CODEGEN_VLIW choice with automatic FLIX generation for xt-clang toolchain

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Copilot · 2026-02-04T18:41:18Z

app/Kconfig


+# Allow compiler to determine whether to generate FLIX instructions.
+choice COMPILER_CODEGEN_VLIW
+        default COMPILER_CODEGEN_VLIW_AUTO if "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "xt-clang"


Inconsistent indentation: The indentation uses spaces here, but the rest of the file uses tabs (see lines 2 and 5). For consistency with the existing code, this line should use a tab instead of spaces.

Suggested change

default COMPILER_CODEGEN_VLIW_AUTO if "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "xt-clang"

default COMPILER_CODEGEN_VLIW_AUTO if "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "xt-clang"

app/Kconfig

dcpleung · 2026-02-04T19:08:39Z

Need this to be merged first before moving Zephyr to latest: zephyrproject-rtos/zephyr#103465

This sets the toolchain kconfig to allow generating FLIX instructions as it is disabled by default on Zephyr upstream. Signed-off-by: Daniel Leung <daniel.leung@intel.com>

abonislawski reviewed Feb 2, 2026

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lgirdwood reviewed Feb 2, 2026

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dcpleung force-pushed the toolchain/allow_flix_gen branch from 39f5acd to 2a5f714 Compare February 4, 2026 18:34

dcpleung marked this pull request as ready for review February 4, 2026 18:35

dcpleung requested review from dbaluta, kv2019i, lbetlej, mmaka1 and plbossart as code owners February 4, 2026 18:35

Copilot AI review requested due to automatic review settings February 4, 2026 18:35

Copilot started reviewing on behalf of dcpleung February 4, 2026 18:37 View session

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app: kconfig: allow FLIX generation

94bd48b

This sets the toolchain kconfig to allow generating FLIX instructions as it is disabled by default on Zephyr upstream. Signed-off-by: Daniel Leung <daniel.leung@intel.com>

dcpleung force-pushed the toolchain/allow_flix_gen branch from 2a5f714 to 94bd48b Compare February 4, 2026 19:17

	default COMPILER_CODEGEN_VLIW_AUTO if "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "xt-clang"
	default COMPILER_CODEGEN_VLIW_AUTO if "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "xt-clang"

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