[Skiboot] [RESEND PATCH v2 1/4] npu2: Rework phb-index assignments for virtual PHBs

Frederic Barrat fbarrat at linux.ibm.com
Thu Jan 23 02:03:33 AEDT 2020

Until now, opencapi PHBs were not using the 'ibm,phb-index' property,
as it was thought unnecessary. For nvlink, a phb-index was associated
to the npu when parsing hdat data, and the nvlink PHB was reusing the
same value.

It turns out it helps to have the 'ibm,phb-index' property for
opencapi PHBs after all. Otherwise it can lead to wrong results on
platforms like mihawk when trying to match entries in the slot
table. We end up with an opencapi device inheriting wrong properties
in the device tree, because match_slot_phb_entry() default to
phb-index 0 if it cannot find the property. Though it doesn't seem to
cause any harm, it's wrong and a future patch is expected to start
using the slot table for opencapi, so it needs fixing.

The twist is that with opencapi, we can have multiple virtual PHBs for
a single NPU on P9. There's one PHB per (opencapi) brick. Therefore
there's no 1-to-1 mapping between the NPU and PHB index and it no
longer makes sense to associate a phb-index to a npu.

With this patch, opencapi PHBs created under a NPU use a fixed mapping
for their phb-index, based on the brick index. The range of possible
values is 7 to 12. Because there can only be one nvlink PHB per NPU,
it is always using a phb-index of 7.

A side effect is that 2 virtual PHBs on 2 different chips can have the
same phb-index, which is similar to what happens for 'real' PCI PHBs,
but is different from what was happening on a nvlink-only witherspoon
so far.

Reviewed-by: Reza Arbab <arbab at linux.ibm.com>
Reviewed-by: Andrew Donnellan <ajd at linux.ibm.com>
Signed-off-by: Frederic Barrat <fbarrat at linux.ibm.com>

Resending series after rebasing to current master, since it was no
longer applying cleanly. I've picked up the Reviewed-by's from v2. No
code change.

 - add comment summarizing the commit msg in the code (Andrew)
 - move the axone changes to separate patch

 hw/npu2-common.c   |  1 -
 hw/npu2-opencapi.c |  2 ++
 hw/npu2.c          |  2 +-
 include/npu2.h     | 20 +++++++++++++++++++-
 4 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/hw/npu2-common.c b/hw/npu2-common.c
index 51ecd0c8..4e5b104e 100644
--- a/hw/npu2-common.c
+++ b/hw/npu2-common.c
@@ -537,7 +537,6 @@ static struct npu2 *setup_npu(struct dt_node *dn)
 	npu->index = dt_prop_get_u32(dn, "ibm,npu-index");
 	npu->chip_id = gcid;
 	npu->xscom_base = dt_get_address(dn, 0, NULL);
-	npu->phb_index = dt_prop_get_u32(dn, "ibm,phb-index");
 	npu->i2c_pin_mode = ~0; // input mode by default
diff --git a/hw/npu2-opencapi.c b/hw/npu2-opencapi.c
index 19589c92..133d78b9 100644
--- a/hw/npu2-opencapi.c
+++ b/hw/npu2-opencapi.c
@@ -1734,6 +1734,8 @@ static void setup_device(struct npu2_dev *dev)
 	dt_add_property_strings(dn_phb, "device_type", "pciex");
 	dt_add_property(dn_phb, "reg", mm_win, sizeof(mm_win));
 	dt_add_property_cells(dn_phb, "ibm,npu-index", dev->npu->index);
+	dt_add_property_cells(dn_phb, "ibm,phb-index",
+			      npu2_get_phb_index(dev->brick_index));
 	dt_add_property_cells(dn_phb, "ibm,chip-id", dev->npu->chip_id);
 	dt_add_property_cells(dn_phb, "ibm,xscom-base", dev->npu->xscom_base);
 	dt_add_property_cells(dn_phb, "ibm,npcq", dev->npu->dt_node->phandle);
diff --git a/hw/npu2.c b/hw/npu2.c
index aeb7c49e..be442baa 100644
--- a/hw/npu2.c
+++ b/hw/npu2.c
@@ -1484,7 +1484,7 @@ int npu2_nvlink_init_npu(struct npu2 *npu)
 	dt_add_property_strings(np, "device_type", "pciex");
 	dt_add_property(np, "reg", reg, sizeof(reg));
-	dt_add_property_cells(np, "ibm,phb-index", npu->phb_index);
+	dt_add_property_cells(np, "ibm,phb-index", npu2_get_phb_index(0));
 	dt_add_property_cells(np, "ibm,npu-index", npu->index);
 	dt_add_property_cells(np, "ibm,chip-id", npu->chip_id);
 	dt_add_property_cells(np, "ibm,xscom-base", npu->xscom_base);
diff --git a/include/npu2.h b/include/npu2.h
index d2a3430e..309a7c7f 100644
--- a/include/npu2.h
+++ b/include/npu2.h
@@ -178,7 +178,6 @@ struct npu2 {
 	/* NVLink */
 	struct phb	phb_nvlink;
-	uint32_t	phb_index;
 	/* OCAPI */
 	uint64_t	i2c_port_id_ocapi;
@@ -256,4 +255,23 @@ int64_t npu2_set_relaxed_order(struct phb *phb, uint32_t gcid, int pec,
 void npu2_opencapi_set_broken(struct npu2 *npu, int brick);
+#define NPU2_PHB_INDEX_BASE 7
+/* to avoid conflicts with PCI and for historical reasons */
+static inline int npu2_get_phb_index(unsigned int brick_index)
+	/*
+	 * There's one virtual PHB per brick with opencapi, so we no
+	 * longer have a 1-to-1 mapping between a NPU and a virtual
+	 * PHB. And we want a static phb-index, as it is needed to use
+	 * a slot table on some platforms. So we associate a per-chip
+	 * phb-index based on the brick index.
+	 *
+	 * nvlink only creates one virtual PHB per chip, so it is
+	 * treated as if using brick 0, which is never used by
+	 * opencapi.
+	 */
+	return NPU2_PHB_INDEX_BASE + brick_index;
 #endif /* __NPU2_H */

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