[fix] Build requested CUDA archs and matching cuDSS archive on Jetson

[vikuznetsov-nvidia]

Jetson builds had two problems when cuNLS was built on its own or pulled into another project:

CUDA architectures: cuNLS always overwrote the caller's CMAKE_CUDA_ARCHITECTURES with 75;80;86;89. On Orin there was no sm_87 code, so kernels failed to launch or JIT-compiled from PTX that the driver couldn't load. The default now applies only when the caller hasn't set the variable. The same change is made in examples/ and tests/install_test/.
cuDSS archive: the cuDSS download was chosen from the host CPU, which gave Orin the linux-sbsa archive. It is now chosen from the CUDA toolkit's target directory (x86_64, aarch64 or sbsa). A new CUDSS_PLATFORM cache variable overrides it.
nvcc fallback: /usr/local/cuda/bin/nvcc is now used only when neither CMAKE_CUDA_COMPILER nor CUDACXX is set.
The README and the Sphinx installation docs describe the new behavior.

Tested in cuVSLAM PR CI with cuNLS tests enabled: x86_64 and Orin pass all tests (Orin 338/338).

Summary by CodeRabbit

• Build Configuration

  • Preserves CUDA compiler and architecture settings supplied by the build environment. Uses /usr/local/cuda/bin/nvcc as a fallback only when no compiler is selected and that executable is available.
  • Selects a cuDSS platform based on the CUDA Toolkit target, with an option to choose a platform explicitly. If the toolkit does not identify a target, x86-64 builds default to linux-x86_64; other architectures may require an explicit selection.

• Documentation

  • Adds guidance for CUDA configuration, native Jetson Orin builds, and cuDSS platform selection, including platform detection and fallback behavior.

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📒 Files selected for processing (3)

• README.md
• cmake/AddCUDSS.cmake
• docs/sphinx/installation.rst

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• README.md
• cmake/AddCUDSS.cmake

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📝 Walkthrough

Walkthrough

CMake now preserves caller-provided CUDA compiler and architecture settings, applies defaults when they are undefined, and supports selecting cuDSS archives by CUDA Toolkit target platform. The build documentation describes these settings and platform options.

Changes

CUDA and cuDSS configuration

Layer / File(s)	Summary
CUDA compiler and architecture defaults CMakeLists.txt, examples/CMakeLists.txt, tests/install_test/CMakeLists.txt, README.md	The CMake configurations apply CUDA architecture defaults only when CMAKE_CUDA_ARCHITECTURES is undefined. They use /usr/local/cuda/bin/nvcc only when CMAKE_CUDA_COMPILER and CUDACXX are unset and the path exists. The README documents this behavior and gives an SM 87 cubin example.
cuDSS platform selection and archive URL cmake/AddCUDSS.cmake, CMakeLists.txt	CUDSS_PLATFORM defaults to auto and is passed to add_cudss. The function resolves auto from CUDA Toolkit include paths, uses the Toolkit major version in the archive tag, and constructs the download URL from the selected platform and tag.
cuDSS platform selection documentation README.md, docs/sphinx/installation.rst	The documentation describes automatic platform selection, fallback behavior, and explicit platform overrides.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~12 minutes

Change: Bug fix

Suggested reviewers: alexkorovko

Merge Risk: ⚪ Minimal · up to e1f40

Caller-selected CUDA settings are preserved, and cuDSS platform selection has documented fallbacks and overrides. No actionable merge blocker is established; the change is ready for normal build checks.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main changes: preserving requested CUDA architectures and selecting the matching cuDSS archive for Jetson builds.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Inline comments:
Review comments at @cmake/AddCUDSS.cmake:
- Line 58: Update the CUDSS platform auto-detection around the
_cudss_include_dir match so scattered toolkit include paths such as /usr/include
fall back to native x86_64. Keep requiring an explicit CUDSS_PLATFORM for
aarch64 when the installation does not identify whether it targets linux-aarch64
or linux-sbsa.

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📒 Files selected for processing (6)

• CMakeLists.txt
• README.md
• cmake/AddCUDSS.cmake
• docs/sphinx/installation.rst
• examples/CMakeLists.txt
• tests/install_test/CMakeLists.txt

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