[PATCH v2 2/3] cxl/acpi: Make the XOR calculations available for testing

[Alison Schofield <alison.schofield@intel.com>]

In preparation for adding a test module that can exercise the address
translation functions performed by the CXL Driver, refactor the XOR
implementation like this:

- Extract the core calculation into a standalone helper function,
- Mark the new helper function as __mock_export to make it available
  to test modules while keeping it otherwise static,
- Enhance the parameter validation since this new function will be
  called from a test module with no guarantee of valid rameters.
- Move the define of struct cxl_cxims_data to include/linux/acpi.h
  so the test module can build and pass xormap data.

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
---
 drivers/cxl/acpi.c   | 35 ++++++++++++++++++++++++-----------
 include/linux/acpi.h |  7 +++++++
 2 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index 26c494704437..f924058dbd4c 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -11,11 +11,6 @@
 #include "cxlpci.h"
 #include "cxl.h"
 
-struct cxl_cxims_data {
-	int nr_maps;
-	u64 xormaps[] __counted_by(nr_maps);
-};
-
 /*
  * There is one CXIMS, therefore one set of XOR maps, that all CXL Windows with
  * the same host bridge granularity share. The number of maps to apply at address
@@ -28,20 +23,31 @@ static const int hbiw_to_nr_maps[HBIW_TO_NR_MAPS_SIZE] = {
 	[1] = 0, [2] = 1, [3] = 0, [4] = 2, [6] = 1, [8] = 3, [12] = 2, [16] = 4
 };
 
+static const int valid_hbiw[] = { 1, 2, 3, 4, 6, 8, 12, 16 };
+
 static const guid_t acpi_cxl_qtg_id_guid =
 	GUID_INIT(0xF365F9A6, 0xA7DE, 0x4071,
 		  0xA6, 0x6A, 0xB4, 0x0C, 0x0B, 0x4F, 0x8E, 0x52);
 
-static u64 cxl_apply_xor_maps(struct cxl_root_decoder *cxlrd, u64 addr)
+__mock_export u64 cxl_do_xormap_calc(struct cxl_cxims_data *cximsd, u64 addr, int hbiw)
 {
-	int nr_maps_to_apply = hbiw_to_nr_maps[cxlrd->cxlsd.nr_targets];
-	struct cxl_cxims_data *cximsd = cxlrd->platform_data;
+	int nr_maps_to_apply = -1;
 	u64 val;
 	int pos;
 
-	/* No xormaps for host bridge interleave ways of 1 or 3 */
-	if (!nr_maps_to_apply)
-		return addr;
+	/*
+	 * Strictly validate hbiw since this function is used for testing and
+	 * that nullifies any expectation of trusted parameters from the CXL
+	 * Region Driver.
+	 */
+	for (int i = 0; i < ARRAY_SIZE(valid_hbiw); i++) {
+		if (valid_hbiw[i] == hbiw) {
+			nr_maps_to_apply = hbiw_to_nr_maps[hbiw];
+			break;
+		}
+	}
+	if (nr_maps_to_apply == -1 || nr_maps_to_apply > cximsd->nr_maps)
+		return ULLONG_MAX;
 
 	/*
 	 * In regions using XOR interleave arithmetic the CXL HPA may not
@@ -73,6 +79,13 @@ static u64 cxl_apply_xor_maps(struct cxl_root_decoder *cxlrd, u64 addr)
 	return addr;
 }
 
+static u64 cxl_apply_xor_maps(struct cxl_root_decoder *cxlrd, u64 addr)
+{
+	struct cxl_cxims_data *cximsd = cxlrd->platform_data;
+
+	return cxl_do_xormap_calc(cximsd, addr, cxlrd->cxlsd.nr_targets);
+}
+
 struct cxl_cxims_context {
 	struct device *dev;
 	struct cxl_root_decoder *cxlrd;
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 1c5bb1e887cd..78e639a529c2 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1616,4 +1616,11 @@ static inline bool acpi_node_backed_by_real_pxm(int nid)
 }
 #endif
 
+#if IS_ENABLED(CONFIG_CXL_ACPI)
+struct cxl_cxims_data {
+	int nr_maps;
+	u64 xormaps[] __counted_by(nr_maps);
+};
+#endif
+
 #endif	/*_LINUX_ACPI_H*/
-- 
2.37.3