Fix gfx95 bpreshuffle FP8 activation scale layout (#29275)

Co-authored-by: sunxxuns <126995791+sunxxuns@users.noreply.github.com>

test/registered/unit/layers/test_fp8_bpreshuffle_scale.py

@@ -0,0 +1,51 @@
+import unittest
+
+import torch
+
+from sglang.srt.layers.quantization.fp8_utils import (
+    materialize_bpreshuffle_fp8_scale,
+    materialize_bpreshuffle_fp8_scale_tuple,
+)
+from sglang.test.ci.ci_register import register_cpu_ci
+from sglang.test.test_utils import CustomTestCase
+
+register_cpu_ci(est_time=5, suite="base-a-test-cpu")
+
+
+class TestBpreshuffleScaleMaterialization(CustomTestCase):
+    def test_materializes_transposed_physical_storage(self):
+        scale = torch.arange(12, dtype=torch.float32).reshape(3, 4)
+
+        materialized = materialize_bpreshuffle_fp8_scale(scale)
+
+        self.assertTrue(torch.equal(materialized, scale))
+        self.assertEqual(materialized.shape, scale.shape)
+        self.assertEqual(materialized.stride(), (1, scale.shape[0]))
+        self.assertTrue(materialized.t().is_contiguous())
+
+    def test_materialization_is_idempotent_for_bpreshuffle_layout(self):
+        scale = torch.arange(12, dtype=torch.float32).reshape(3, 4)
+        materialized = materialize_bpreshuffle_fp8_scale(scale)
+
+        rematerialized = materialize_bpreshuffle_fp8_scale(materialized)
+
+        self.assertTrue(torch.equal(rematerialized, scale))
+        self.assertEqual(rematerialized.stride(), materialized.stride())
+
+    def test_tuple_helper_keeps_extra_tuple_payload(self):
+        q_input = torch.ones((3, 8), dtype=torch.float32)
+        scale = torch.arange(12, dtype=torch.float32).reshape(3, 4)
+        bf16_side = torch.ones((3, 8), dtype=torch.bfloat16)
+
+        q_out, scale_out, bf16_out = materialize_bpreshuffle_fp8_scale_tuple(
+            (q_input, scale, bf16_side)
+        )
+
+        self.assertIs(q_out, q_input)
+        self.assertIs(bf16_out, bf16_side)
+        self.assertTrue(torch.equal(scale_out, scale))
+        self.assertEqual(scale_out.stride(), (1, scale.shape[0]))
+
+
+if __name__ == "__main__":
+    unittest.main()