tests: riscv: pmp: Make permission change tests dynamic

The existing PMP permission tests relied on hardcoded region indices
(e.g., index 0 or 2). This makes the tests fragile and dependent
on the exact memory attribute region setup.

This change refactors the tests to dynamically determine region counts
and indices based on the output of `mem_attr_get_regions()`:

-   `test_pmp_change_perm_invalid_permission`: Uses the last valid
    region index to test invalid permission flags.
-   `test_pmp_change_perm_invalid_region_index`: Uses the total number
    of regions as the out-of-bounds index.
-   `test_successful_permission_change`: Locates the index of the
    target test region (`dt_regions[0]`) by matching its base address
    and size. The test now also inverts the X bit of the current
    permissions to ensure a change is applied and verified.

These changes make the tests more robust and less dependent on a
specific static configuration.

Signed-off-by: Firas Sammoura <[email protected]>

Author: fsammoura1980

tests/arch/riscv/pmp/mem-attr-entries/src/main.c

@@ -127,33 +127,53 @@ ZTEST(riscv_pmp_memattr_entries, test_dt_pmp_perm_conversion)
 
 ZTEST(riscv_pmp_memattr_entries, test_pmp_change_perm_invalid_permission)
 {
+	const struct mem_attr_region_t *region;
+	size_t num_regions = mem_attr_get_regions(&region);
+	size_t idx = num_regions - 1;
+
 	/* Invalid permission: 0x08 (bit 3) is outside of R|W|X (0x7) mask */
-	zassert_equal(z_riscv_pmp_change_permissions(0, 0x08), -EINVAL,
+	zassert_equal(z_riscv_pmp_change_permissions(idx, 0x08), -EINVAL,
 		      "Should return -EINVAL for invalid permission bits.");
 }
 
 ZTEST(riscv_pmp_memattr_entries, test_pmp_change_perm_invalid_region_index)
 {
-	/* region_idx = 2, which is out of bounds */
-	size_t idx = 2;
+	const struct mem_attr_region_t *region;
+	size_t num_regions = mem_attr_get_regions(&region);
+	size_t invalid_idx = num_regions;
 
-	zassert_equal(z_riscv_pmp_change_permissions(idx, PMP_R), -EINVAL,
+	zassert_equal(z_riscv_pmp_change_permissions(invalid_idx, PMP_R), -EINVAL,
 		      "Should return -EINVAL for region index out of bounds.");
 }
 
 ZTEST(riscv_pmp_memattr_entries, test_successful_permission_change)
 {
-	const uint8_t new_perm = 0x03; /* Read (0x1) | Write (0x2) */
-	const size_t idx = 0;
+	const struct mem_attr_region_t *region;
+	size_t num_regions = mem_attr_get_regions(&region);
+	size_t idx;
+
+	/* Find the matching index of memory attribute region for dt_regions[0] */
+	for (idx = 0; idx < num_regions; ++idx) {
+		if ((region[idx].dt_addr == dt_regions[0].base) &&
+		    (region[idx].dt_size == dt_regions[0].size)) {
+			break;
+		}
+	}
 
-	zassert_not_equal(new_perm, dt_regions[idx].perm,
-			  "Ensure new permission is different from existing permission");
+	zassert_not_equal(idx, num_regions,
+			  "No matching memory attribute region found for dt_regions[0].");
 
-	int ret = z_riscv_pmp_change_permissions(idx, new_perm);
+	/* Store original permission to revert later if needed, and calculate new permission */
+	uint8_t original_perm = dt_regions[0].perm;
+	uint8_t new_perm = PMP_X ^ original_perm; /* Toggle X bit */
 
-	dt_regions[idx].perm = new_perm;
+	/* Update the expectations */
+	dt_regions[0].perm = new_perm;
 
-	zassert_equal(ret, 0, "Function should return 0 on success.");
+	/* Apply the permission change to the hardware */
+	int ret = z_riscv_pmp_change_permissions(idx, new_perm);
+
+	zassert_equal(ret, 0, "z_riscv_pmp_change_permissions should return 0 on success.");
 
 	const size_t num_pmpcfg_regs = CONFIG_PMP_SLOTS / sizeof(unsigned long);
 	const size_t num_pmpaddr_regs = CONFIG_PMP_SLOTS;
@@ -192,6 +212,10 @@ ZTEST(riscv_pmp_memattr_entries, test_successful_permission_change)
 			     "found.",
 			     i + 1, dt_regions[i].base, dt_regions[i].size, dt_regions[i].perm);
 	}
+
+	/* Restore original permissions to leave system in original state */
+	z_riscv_pmp_change_permissions(idx, original_perm);
+	dt_regions[0].perm = original_perm;
 }
 
 ZTEST_SUITE(riscv_pmp_memattr_entries, NULL, NULL, NULL, NULL, NULL);