[Skiboot] [PATCH] npu2: Add performance tuning SCOM inits

[Reza Arbab]

Peer-to-peer GPU bandwidth latency testing has produced some tunable
values that improve performance. Add them to our device initialization.

File these under things that need to be cleaned up with nice #defines
for the register names and bitfields when we get time.

A few of the settings are dependent on the system's particular NVLink
topology, so introduce a helper to determine how many links go to a
single GPU.

Signed-off-by: Reza Arbab <arbab at linux.vnet.ibm.com>
---
 hw/npu2.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 96 insertions(+), 1 deletion(-)

diff --git a/hw/npu2.c b/hw/npu2.c
index a0cf41f..7ed2443 100644
--- a/hw/npu2.c
+++ b/hw/npu2.c
@@ -683,9 +683,73 @@ static int npu2_dn_fixup(struct phb *phb,
 	return 0;
 }
 
+static int npu2_links_per_gpu(struct phb *phb,
+			      struct pci_device *pd,
+			      void *data)
+{
+	struct npu2 *p = phb_to_npu2_nvlink(phb);
+	struct npu2_dev *dev;
+	int *nlinks = (int *)data;
+
+	dev = npu2_bdf_to_dev(p, pd->bdfn);
+	assert(dev);
+
+	if (dev->nvlink.phb && dev->nvlink.pd && dev->nvlink.pd->dn) {
+		const struct dt_property *prop;
+		int n;
+
+		/* The link count is the number of phandles in "ibm,npu" */
+		prop = dt_find_property(dev->nvlink.pd->dn, "ibm,npu");
+		if (!prop)
+			return 0;
+
+		/* Count could vary by gpu, so find the max */
+		n = prop->len / sizeof(uint32_t);
+		if (n > *nlinks)
+			*nlinks = n;
+	}
+
+	return 0;
+}
+
+static void npu2_phb_fixup_scominit(struct dt_node *dn, int links_per_gpu)
+{
+	uint32_t gcid = dt_get_chip_id(dn);
+	uint64_t val, mask;
+
+	/*
+	 * MRBSP settings for 2- and 3-link GPU systems. These can improve
+	 * GPU peer-to-peer fully ordered write performance.
+	 */
+	if (links_per_gpu == 3) {
+		val = PPC_BIT(30) | PPC_BIT(34) | PPC_BIT(36) | PPC_BIT(37) |
+		      PPC_BIT(44) | PPC_BIT(45);
+		mask = PPC_BITMASK(28,39) | PPC_BITMASK(44,47);
+	} else if (links_per_gpu == 2) {
+		val = PPC_BIT(46) | PPC_BIT(47);
+		mask = PPC_BITMASK(44,47);
+	} else
+		return;
+
+	xscom_write_mask(gcid, 0x50110c0, val, mask);
+	xscom_write_mask(gcid, 0x50112c0, val, mask);
+	xscom_write_mask(gcid, 0x50114c0, val, mask);
+}
+
 static void npu2_phb_final_fixup(struct phb *phb)
 {
+	int links_per_gpu = 0;
+	struct dt_node *np;
+
 	pci_walk_dev(phb, NULL, npu2_dn_fixup, NULL);
+
+	/*
+	 * Now that the emulated devices are bound to the real ones, we can
+	 * determine links_per_gpu and do some final init.
+	 */
+	pci_walk_dev(phb, NULL, npu2_links_per_gpu, &links_per_gpu);
+	dt_for_each_compatible(dt_root, np, "ibm,power9-npu")
+		npu2_phb_fixup_scominit(np, links_per_gpu);
 }
 
 static void npu2_init_ioda_cache(struct npu2 *p)
@@ -1275,7 +1339,7 @@ static void npu2_probe_phb(struct dt_node *dn)
 	struct proc_chip *proc_chip;
 	struct dt_node *np;
 	uint32_t gcid, scom, index, phb_index, links;
-	uint64_t reg[2], mm_win[2];
+	uint64_t reg[2], mm_win[2], val;
 	char *path;
 
 	/* Abort if any OpenCAPI links detected */
@@ -1331,6 +1395,37 @@ static void npu2_probe_phb(struct dt_node *dn)
 	xscom_write_mask(gcid, 0x5011510, PPC_BIT(0), PPC_BIT(0));
 	xscom_write_mask(gcid, 0x5011530, PPC_BIT(0), PPC_BIT(0));
 
+	/*
+	 * Enable relaxed ordering for peer-to-peer reads
+	 */
+	val = PPC_BIT(5) | PPC_BIT(29);
+	xscom_write_mask(gcid, 0x501100c, val, val);
+	xscom_write_mask(gcid, 0x501103c, val, val);
+	xscom_write_mask(gcid, 0x501106c, val, val);
+	xscom_write_mask(gcid, 0x501109c, val, val);
+	xscom_write_mask(gcid, 0x501120c, val, val);
+	xscom_write_mask(gcid, 0x501123c, val, val);
+	xscom_write_mask(gcid, 0x501126c, val, val);
+	xscom_write_mask(gcid, 0x501129c, val, val);
+	xscom_write_mask(gcid, 0x501140c, val, val);
+	xscom_write_mask(gcid, 0x501143c, val, val);
+	xscom_write_mask(gcid, 0x501146c, val, val);
+	xscom_write_mask(gcid, 0x501149c, val, val);
+
+	val = PPC_BIT(6) | PPC_BIT(7) | PPC_BIT(11);
+	xscom_write_mask(gcid, 0x5011009, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011039, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011069, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011099, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011209, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011239, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011269, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011299, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011409, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011439, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011469, val, PPC_BITMASK(6,11));
+	xscom_write_mask(gcid, 0x5011499, val, PPC_BITMASK(6,11));
+
 	index = dt_prop_get_u32(dn, "ibm,npu-index");
 	phb_index = dt_prop_get_u32(dn, "ibm,phb-index");
 	links = dt_prop_get_u32(dn, "ibm,npu-links");
-- 
1.8.3.1