[PATCH V6 8/8] PCI/P2PDMA: Add a 10-bit tag check in P2PDMA

[Dongdong Liu <liudongdong3@huawei.com>]

Add a 10-Bit Tag check in the P2PDMA code to ensure that a device with
10-Bit Tag Requester doesn't interact with a device that does not
support 10-BIT tag Completer. Before that happens, the kernel should
emit a warning saying to enable a ”pci=disable_10bit_tag=“ kernel
parameter.

Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
---
 drivers/pci/p2pdma.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 50cdde3..bd93840 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -19,6 +19,7 @@
 #include <linux/random.h>
 #include <linux/seq_buf.h>
 #include <linux/xarray.h>
+#include "pci.h"
 
 enum pci_p2pdma_map_type {
 	PCI_P2PDMA_MAP_UNKNOWN = 0,
@@ -541,6 +542,39 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
 	return map_type;
 }
 
+
+static bool check_10bit_tags_vaild(struct pci_dev *a, struct pci_dev *b,
+				   bool verbose)
+{
+	bool req;
+	bool comp;
+	u16 ctl2;
+
+	if (a->is_virtfn) {
+#ifdef CONFIG_PCI_IOV
+		req = !!(a->physfn->sriov->ctrl &
+			 PCI_SRIOV_CTRL_VF_10BIT_TAG_REQ_EN);
+#endif
+	} else {
+		pcie_capability_read_word(a, PCI_EXP_DEVCTL2, &ctl2);
+		req = !!(ctl2 & PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN);
+	}
+
+	comp = !!(b->pcie_devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_COMP);
+	if (req && (!comp)) {
+		if (verbose) {
+			pci_warn(a, "cannot be used for peer-to-peer DMA as 10-Bit Tag Requester enable is set in device (%s), but peer device (%s) does not support the 10-Bit Tag Completer\n",
+				 pci_name(a), pci_name(b));
+
+			pci_warn(a, "to disable 10-Bit Tag Requester for this device, add the kernel parameter: pci=disable_10bit_tag=%s\n",
+				 pci_name(a));
+		}
+		return false;
+	}
+
+	return true;
+}
+
 /**
  * pci_p2pdma_distance_many - Determine the cumulative distance between
  *	a p2pdma provider and the clients in use.
@@ -579,6 +613,10 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
 			return -1;
 		}
 
+		if (!check_10bit_tags_vaild(pci_client, provider, verbose) ||
+		    !check_10bit_tags_vaild(provider, pci_client, verbose))
+			not_supported = true;
+
 		map = calc_map_type_and_dist(provider, pci_client, &distance,
 					     verbose);
 
-- 
2.7.4