[PATCH v3 03/14] PCI/P2PDMA: Add constants for map type results to upstream_bridge_distance()

Logan Gunthorpe
2019-08-12T17:31:05Z

Add constant flags to indicate how two devices will be mapped or if they
are unsupported. upstream_bridge_distance() will now return the
mapping type and the distance in a passed-by-reference argument.

This helps annotate the code better, but the main reason is so we can use
the information to store the required mapping method in an xarray.

Link: https://lore.kernel.org/r/20190730163545.4915-4-logang@deltatee.com
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
---
drivers/pci/p2pdma.c | 95 +++++++++++++++++++++++++++-----------------
1 file changed, 58 insertions(+), 37 deletions(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 93fbda14f4a9..8f0688201aec 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -20,6 +20,13 @@
#include <linux/seq_buf.h>
#include <linux/iommu.h>

+enum pci_p2pdma_map_type {
+ PCI_P2PDMA_MAP_UNKNOWN = 0,
+ PCI_P2PDMA_MAP_NOT_SUPPORTED,
+ PCI_P2PDMA_MAP_BUS_ADDR,
+ PCI_P2PDMA_MAP_THRU_HOST_BRIDGE,
+};
+
struct pci_p2pdma {
struct gen_pool *pool;
bool p2pmem_published;
@@ -313,34 +320,33 @@ 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
+ * PCI_P2PDMA_MAP_NOT_SUPPORTED.
+ *
+ * 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,
+ * this function will return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE.
*
- * 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.
+ * If either bridge is not on the whitelist this function returns
+ * PCI_P2PDMA_MAP_NOT_SUPPORTED.
*
- * 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.
- * In this case, a list of all infringing bridge addresses will be
- * populated in acs_list (assuming it's non-null) for printk purposes.
+ * If a bridge which has any ACS redirection bits set is in the path,
+ * acs_redirects will be set to true. In this case, a list of all infringing
+ * bridge addresses will be populated in acs_list (assuming it's non-null)
+ * for printk purposes.
*/
-static int upstream_bridge_distance(struct pci_dev *provider,
- struct pci_dev *client,
- struct seq_buf *acs_list)
+static enum pci_p2pdma_map_type
+upstream_bridge_distance(struct pci_dev *provider, struct pci_dev *client,
+ int *dist, bool *acs_redirects, struct seq_buf *acs_list)
{
struct pci_dev *a = provider, *b = client, *bb;
int dist_a = 0;
int dist_b = 0;
int acs_cnt = 0;

+ if (acs_redirects)
+ *acs_redirects = false;
+
/*
* Note, we don't need to take references to devices returned by
* pci_upstream_bridge() seeing we hold a reference to a child
@@ -369,15 +375,18 @@ static int upstream_bridge_distance(struct pci_dev *provider,
dist_a++;
}

+ if (dist)
+ *dist = dist_a + dist_b;
+
/*
* Allow the connection if both devices are on a whitelisted root
* complex, but add an arbitrary large value to the distance.
*/
if (root_complex_whitelist(provider) &&
root_complex_whitelist(client))
- return 0x1000 + dist_a + dist_b;
+ return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE;

- return -1;
+ return PCI_P2PDMA_MAP_NOT_SUPPORTED;

check_b_path_acs:
bb = b;
@@ -394,33 +403,44 @@ static int upstream_bridge_distance(struct pci_dev *provider,
bb = pci_upstream_bridge(bb);
}

- if (acs_cnt)
- return -2;
+ if (dist)
+ *dist = dist_a + dist_b;

- return dist_a + dist_b;
+ if (acs_cnt) {
+ if (acs_redirects)
+ *acs_redirects = true;
+
+ return PCI_P2PDMA_MAP_NOT_SUPPORTED;
+ }
+
+ return PCI_P2PDMA_MAP_BUS_ADDR;
}

-static int upstream_bridge_distance_warn(struct pci_dev *provider,
- struct pci_dev *client)
+static enum pci_p2pdma_map_type
+upstream_bridge_distance_warn(struct pci_dev *provider, struct pci_dev *client,
+ int *dist)
{
struct seq_buf acs_list;
+ bool acs_redirects;
int ret;

seq_buf_init(&acs_list, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);
if (!acs_list.buffer)
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",
+ ret = upstream_bridge_distance(provider, client, dist, &acs_redirects,
+ &acs_list);
+ if (acs_redirects) {
+ 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 == PCI_P2PDMA_MAP_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));
}

@@ -452,7 +472,8 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
{
bool not_supported = false;
struct pci_dev *pci_client;
- int distance = 0;
+ int total_dist = 0;
+ int distance;
int i, ret;

if (num_clients == 0)
@@ -477,26 +498,26 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,

if (verbose)
ret = upstream_bridge_distance_warn(provider,
- pci_client);
+ pci_client, &distance);
else
ret = upstream_bridge_distance(provider, pci_client,
- NULL);
+ &distance, NULL, NULL);

pci_dev_put(pci_client);

- if (ret < 0)
+ if (ret == PCI_P2PDMA_MAP_NOT_SUPPORTED)
not_supported = true;

if (not_supported && !verbose)
break;

- distance += ret;
+ total_dist += distance;
}

if (not_supported)
return -1;

- return distance;
+ return total_dist;
}
EXPORT_SYMBOL_GPL(pci_p2pdma_distance_many);

--
2.20.1