drm/ttm/tests: Add TODO file

List improvements for the test suite with some notes.

Signed-off-by: Karolina Stolarek <[e-mail]>
Reviewed-by: Thomas Hellström <[e-mail]>
Signed-off-by: Arunpravin Paneer Selvam <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/3856fbbea[e-mail]

drivers/gpu/drm/ttm/tests/TODO

···
+TODO
+=====
+
+- Add a test case where the only evictable BO is busy
+- Update eviction tests so they use parametrized "from" memory type
+- Improve mock manager's implementation, e.g. allocate a block of
+  dummy memory that can be used when testing page mapping functions
+- Suggestion: Add test cases with external BOs
+- Suggestion: randomize the number and size of tested buffers in
+  ttm_bo_validate()
+- Agree on the naming convention
+- Rewrite the mock manager: drop use_tt and manage mock memory using
+  drm_mm manager
+
+Notes and gotchas
+=================
+
+- These tests are built and run with a UML kernel, because
+  1) We are interested in hardware-independent testing
+  2) We don't want to have actual DRM devices interacting with TTM
+     at the same time as the test one. Getting these to work in
+     parallel would require some time (...and that's a "todo" in itself!)
+- Triggering ttm_bo_vm_ops callbacks from KUnit (i.e. kernel) might be
+  a challenge, but is worth trying. Look at selftests like
+  i915/gem/selftests/i915_gem_mman.c for inspiration
+- The test suite uses UML where ioremap() call returns NULL, meaning that
+  ttm_bo_ioremap() can't be tested, unless we find a way to stub it