cxl/acpi: Minimize granularity for x1 interleaves

The kernel enforces that region granularity is >= to the top-level
interleave-granularity for the given CXL window. However, when the CXL
window interleave is x1, i.e. non-interleaved at the host bridge level,
then the specified granularity does not matter. Override the window
specified granularity to the CXL minimum so that any valid region
granularity is >= to the root granularity.

Reported-by: Jonathan Cameron <[email protected]>
Reviewed-by: Vishal Verma <[email protected]>
Reviewed-by: Alison Schofield <[email protected]>
Link: https://lore.kernel.org/r/165853776917.2430596.16823264262010844458.stgit@dwillia2-xfh.jf.intel.com
[djbw: add CXL_DECODER_MIN_GRANULARITY per vishal]
Signed-off-by: Dan Williams <[email protected]>

Author: djbw

drivers/cxl/acpi.c

@@ -140,6 +140,12 @@ static int cxl_parse_cfmws(union acpi_subtable_headers *header, void *arg,
 		.end = res->end,
 	};
 	cxld->interleave_ways = ways;
+	/*
+	 * Minimize the x1 granularity to advertise support for any
+	 * valid region granularity
+	 */
+	if (ways == 1)
+		ig = CXL_DECODER_MIN_GRANULARITY;
 	cxld->interleave_granularity = ig;
 
 	rc = cxl_decoder_add(cxld, target_map);

drivers/cxl/cxl.h

@@ -248,6 +248,8 @@ enum cxl_decoder_type {
  */
 #define CXL_DECODER_MAX_INTERLEAVE 16
 
+#define CXL_DECODER_MIN_GRANULARITY 256
+
 /**
  * struct cxl_decoder - Common CXL HDM Decoder Attributes
  * @dev: this decoder's device