[PATCH 01/14] PCI/P2PDMA: Add constants for not-supported result upstream_bridge_distance()

Logan Gunthorpe
2019-07-22T23:09:36Z

Add constant flags to indicate two devices are not supported or whether
the data path goes through the host bridge instead of using the negative
values -1 and -2.

This helps annotate the code better, but the main reason is so we
can cache the result in an xarray which does not allow us to store
negative values.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
drivers/pci/p2pdma.c | 52 ++++++++++++++++++++++++++------------------
1 file changed, 31 insertions(+), 21 deletions(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 234476226529..e8ec86e1dd00 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -273,6 +273,20 @@ static bool root_complex_whitelist(struct pci_dev *dev)
return false;
}

+enum {
+ /*
+ * Thes arbitrary offset are or'd onto the upstream distance
+ * calculation for the following conditions:
+ */
+
+ /* The data path includes the host-bridge */
+ P2PDMA_THRU_HOST_BRIDGE = 0x02000000,
+ /* The data path is forced through the host-bridge due to ACS */
+ P2PDMA_ACS_FORCES_UPSTREAM = 0x04000000,
+ /* The data path is not supported by P2PDMA */
+ P2PDMA_NOT_SUPPORTED = 0x08000000,
+};
+
/*
* Find the distance through the nearest common upstream bridge between
* two PCI devices.
@@ -297,22 +311,17 @@ static bool root_complex_whitelist(struct pci_dev *dev)
* port of the switch, to the common upstream port, back up to the second
* downstream port and then to Device B.
*
- * Any two devices that don't have a common upstream bridge will return -1.
- * In this way devices on separate PCIe root ports will be rejected, which
- * is what we want for peer-to-peer seeing each PCIe root port defines a
- * separate hierarchy domain and there's no way to determine whether the root
- * complex supports forwarding between them.
+ * Any two devices that cannot communicate using p2pdma will return the distance
+ * with the flag P2PDMA_NOT_SUPPORTED.
*
- * In the case where two devices are connected to different PCIe switches,
- * this function will still return a positive distance as long as both
- * switches eventually have a common upstream bridge. Note this covers
- * the case of using multiple PCIe switches to achieve a desired level of
- * fan-out from a root port. The exact distance will be a function of the
- * number of switches between Device A and Device B.
+ * Any two devices that have a data path that goes through the host bridge
+ * will consult a whitelist. If the host bridges are on the whitelist,
+ * then the distance will be returned with the flag P2PDMA_THRU_HOST_BRIDGE set.
+ * If either bridge is not on the whitelist, the flag P2PDMA_NOT_SUPPORTED will
+ * be set.
*
* If a bridge which has any ACS redirection bits set is in the path
- * then this functions will return -2. This is so we reject any
- * cases where the TLPs are forwarded up into the root complex.
+ * then this functions will flag the result with P2PDMA_ACS_FORCES_UPSTREAM.
* In this case, a list of all infringing bridge addresses will be
* populated in acs_list (assuming it's non-null) for printk purposes.
*/
@@ -359,9 +368,9 @@ static int upstream_bridge_distance(struct pci_dev *provider,
*/
if (root_complex_whitelist(provider) &&
root_complex_whitelist(client))
- return 0x1000 + dist_a + dist_b;
+ return (dist_a + dist_b) | P2PDMA_THRU_HOST_BRIDGE;

- return -1;
+ return (dist_a + dist_b) | P2PDMA_NOT_SUPPORTED;

check_b_path_acs:
bb = b;
@@ -379,7 +388,7 @@ static int upstream_bridge_distance(struct pci_dev *provider,
}

if (acs_cnt)
- return -2;
+ return P2PDMA_NOT_SUPPORTED | P2PDMA_ACS_FORCES_UPSTREAM;

return dist_a + dist_b;
}
@@ -395,16 +404,17 @@ static int upstream_bridge_distance_warn(struct pci_dev *provider,
return -ENOMEM;

ret = upstream_bridge_distance(provider, client, &acs_list);
- if (ret == -2) {
- pci_warn(client, "cannot be used for peer-to-peer DMA as ACS redirect is set between the client and provider (%s)\n",
+ if (ret & P2PDMA_ACS_FORCES_UPSTREAM) {
+ pci_warn(client, "ACS redirect is set between the client and provider (%s)\n",
pci_name(provider));
/* Drop final semicolon */
acs_list.buffer[acs_list.len-1] = 0;
pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
acs_list.buffer);
+ }

- } else if (ret < 0) {
- pci_warn(client, "cannot be used for peer-to-peer DMA as the client and provider (%s) do not share an upstream bridge\n",
+ if (ret & P2PDMA_NOT_SUPPORTED) {
+ pci_warn(client, "cannot be used for peer-to-peer DMA as the client and provider (%s) do not share an upstream bridge or whitelisted host bridge\n",
pci_name(provider));
}

@@ -468,7 +478,7 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,

pci_dev_put(pci_client);

- if (ret < 0)
+ if (ret & P2PDMA_NOT_SUPPORTED)
not_supported = true;

if (not_supported && !verbose)
--
2.20.1