[Skiboot] [PATCH 3/5] nvlink: Add fence mode emulation for NPUs

[Russell Currey]

As NPUs are emulated PCI devices, they do not get physically fenced as real
PCI devices to.  As such, when the device is in a state that it should be
fenced, we need to emulate this behaviour by returning all 1s in config
space reads.

This will be utilised by error injection in subsequent patches.

Signed-off-by: Russell Currey <ruscur at russell.cc>
---
 hw/npu.c      | 7 +++++++
 include/npu.h | 1 +
 2 files changed, 8 insertions(+)

diff --git a/hw/npu.c b/hw/npu.c
index 3a06c04..9440f17 100644
--- a/hw/npu.c
+++ b/hw/npu.c
@@ -390,6 +390,10 @@ static int64_t _npu_dev_cfg_read(struct phb *phb, uint32_t bdfn,
 	/* Data returned upon errors */
 	*data = 0xffffffff;
 
+	/* If fenced, we want to return all 1s, so we're done. */
+	if (p->fenced)
+		return OPAL_SUCCESS;
+
 	/* Retrieve NPU device */
 	dev = npu_dev_cfg_check(p, bdfn, offset, size);
 	if (!dev)
@@ -1680,6 +1684,9 @@ static void npu_create_phb(struct dt_node *dn)
 	p->xscom_base = dt_prop_get_u32(dn, "ibm,xscom-base");
 	p->total_devices = links;
 
+	/* XXX: is there any chance we're *already* fenced? */
+	p->fenced = false;
+
 	/* This is the AT base */
 	p->at_xscom = p->xscom_base + NPU_AT_SCOM_OFFSET;
 	p->at_regs = (void *)dt_get_address(dn, 0, NULL);
diff --git a/include/npu.h b/include/npu.h
index 795b704..5d5135b 100644
--- a/include/npu.h
+++ b/include/npu.h
@@ -167,6 +167,7 @@ struct npu {
 	uint64_t		tve_cache[NPU_NUM_OF_PES];
 
 	bool			tx_zcal_complete[2];
+	bool			fenced;
 
 	struct phb		phb;
 };
-- 
2.6.4