[PATCH 3/3] cxl/acpi: Convert QTG _DSM latencies to picoseconds

[Koichiro Den]

The QTG _DSM expects read and write latencies in picoseconds, as
specified in CXL 3.0, Table 9-30.

The code base originally kept the latencies passed to the QTG _DSM in
picoseconds in effect. Commit 51293c565cf4 ("cxl: Fix incorrect region
perf data calculation") normalized CDAT and host bridge latencies to
nanoseconds, but did not add a conversion back to picoseconds when
constructing the _DSM input. Firmware can therefore select QTG IDs using
understated latencies.

Convert the latencies to picoseconds when constructing the _DSM input
package. Multiply in 64 bits and reject latencies that cannot fit in the
DWORD inputs defined by the specification.

Fixes: 51293c565cf4 ("cxl: Fix incorrect region perf data calculation")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
---
 drivers/cxl/acpi.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index fb09a5ff48c1..b7ce6b59c680 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -231,9 +231,10 @@ cxl_acpi_evaluate_qtg_dsm(acpi_handle handle, struct access_coordinate *coord,
 			  int entries, int *qos_class)
 {
 	union acpi_object *out_obj, *out_buf, *obj;
+	/* QTG _DSM expects latencies in picoseconds. */
 	union acpi_object in_array[4] = {
-		[0].integer = { ACPI_TYPE_INTEGER, coord->read_latency },
-		[1].integer = { ACPI_TYPE_INTEGER, coord->write_latency },
+		[0].integer = { ACPI_TYPE_INTEGER, coord->read_latency * 1000ULL },
+		[1].integer = { ACPI_TYPE_INTEGER, coord->write_latency * 1000ULL },
 		[2].integer = { ACPI_TYPE_INTEGER, coord->read_bandwidth },
 		[3].integer = { ACPI_TYPE_INTEGER, coord->write_bandwidth },
 	};
@@ -251,6 +252,11 @@ cxl_acpi_evaluate_qtg_dsm(acpi_handle handle, struct access_coordinate *coord,
 	if (!entries)
 		return -EINVAL;
 
+	/* Latency inputs must fit in the DWORD fields defined by the spec. */
+	if (coord->read_latency > U32_MAX / 1000 ||
+	    coord->write_latency > U32_MAX / 1000)
+		return -ERANGE;
+
 	out_obj = acpi_evaluate_dsm(handle, &acpi_cxl_qtg_id_guid, 1, 1, &in_obj);
 	if (!out_obj)
 		return -ENXIO;
-- 
2.51.0