[Skiboot-stable] [PATCH v2 1/2] sensors: occ: Fix the GPU detection code

[Gautham R. Shenoy]

From: "Gautham R. Shenoy" <ego at linux.vnet.ibm.com>

commit bebe096ee242 ("sensors: occ: Skip GPU sensors for non-gpu
systems") assumes that presence of "ibm,power9-npu" compatible node
indicates the presence of GPUs. However this is incorrect, as even
OpenCAPI is supported via NPU. Thus ZZ systems, which have OpenCAPI
connectors but not GPUs will have "ibm,power9-npu" compatible nodes.
This results in OPAL creating device-tree entries for the GPU sensors
on ZZ systems which don't even have GPUs.

This patch fixes the GPU detection code in occ-sensors, by first
checking for "ibm,ioda2-npu2-phb" compatible node which indicates the
presence of nvlink. Only if such a node exists, do we check with the
OCC for presence of GPUs on systems to confirm the presence of the
GPU. Otherwise, we cut the GPU sensors.

Thanks to Frederic Barrat <fbarrat at linux.ibm.com> for suggesting
"ibm,ioda2-npu2-phb" for detecting the presence of nvlink GPUs.

cc: skiboot-stable at lists.ozlabs.org
Fixes: commit bebe096ee242 ("sensors: occ: Skip GPU sensors for non-gpu
        systems")
Reported-by: Pavaman Subramaniyam <pavsubra at in.ibm.com>
Tested-by: Pavaman Subramaniyam <pavsubra at in.ibm.com>
Reviewed-by: Vaidyanathan Srinivasan <svaidy at linux.ibm.com>
Reviewed-by: Frederic Barrat <fbarrat at linux.ibm.com>
Signed-off-by: Gautham R. Shenoy <ego at linux.vnet.ibm.com>
---
Change from v1: Fixed max_gpus_per_chip = 3

 hw/occ-sensor.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/hw/occ-sensor.c b/hw/occ-sensor.c
index 524d00f..d97cc33 100644
--- a/hw/occ-sensor.c
+++ b/hw/occ-sensor.c
@@ -521,8 +521,26 @@ bool occ_sensors_init(void)
 	dt_add_property_cells(sg, "#address-cells", 1);
 	dt_add_property_cells(sg, "#size-cells", 0);
 
-	if (dt_find_compatible_node(dt_root, NULL, "ibm,power9-npu"))
-		has_gpu = true;
+	/*
+	 * On POWER9, ibm,ioda2-npu2-phb indicates the presence of a
+	 * GPU NVlink.
+	 */
+	if (dt_find_compatible_node(dt_root, NULL, "ibm,ioda2-npu2-phb")) {
+
+		for_each_chip(chip) {
+			int max_gpus_per_chip = 3, i;
+
+			for(i = 0; i < max_gpus_per_chip; i++) {
+				has_gpu = occ_get_gpu_presence(chip, i);
+
+				if (has_gpu)
+					break;
+			}
+
+			if (has_gpu)
+				break;
+		}
+	}
 
 	for_each_chip(chip) {
 		struct occ_sensor_data_header *hb;
-- 
1.9.4