[PATCH 01/15] NTB: Fix access to link status and control register

[Arindam Nath]

The design of AMD NTB implementation is such that
NTB primary acts as an endpoint device and NTB
secondary is an endpoint device behind a combination
of Switch Upstream and Switch Downstream. Considering
that, the link status and control register needs to
be accessed differently based on the NTB topology.

So in the case of NTB secondary, we first get the
pointer to the Switch Downstream device for the NTB
device. Then we get the pointer to the Switch Upstream
device. Once we have that, we read the Link Status
and Control register to get the correct status of
link at the secondary.

In the case of NTB primary, simply reading the Link
Status and Control register of the NTB device itself
will suffice.

Suggested-by: Jiasen Lin <linjiasen@xxxxxxxx>
Signed-off-by: Arindam Nath <arindam.nath@xxxxxxx>
---
 drivers/ntb/hw/amd/ntb_hw_amd.c | 40 ++++++++++++++++++++++++++++++---
 drivers/ntb/hw/amd/ntb_hw_amd.h |  1 -
 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/drivers/ntb/hw/amd/ntb_hw_amd.c b/drivers/ntb/hw/amd/ntb_hw_amd.c
index e52b300b2f5b..9a60f34a37c2 100644
--- a/drivers/ntb/hw/amd/ntb_hw_amd.c
+++ b/drivers/ntb/hw/amd/ntb_hw_amd.c
@@ -842,6 +842,9 @@ static inline void ndev_init_struct(struct amd_ntb_dev *ndev,
 static int amd_poll_link(struct amd_ntb_dev *ndev)
 {
 	void __iomem *mmio = ndev->peer_mmio;
+	struct pci_dev *pdev = NULL;
+	struct pci_dev *pci_swds = NULL;
+	struct pci_dev *pci_swus = NULL;
 	u32 reg, stat;
 	int rc;
 
@@ -855,10 +858,41 @@ static int amd_poll_link(struct amd_ntb_dev *ndev)
 
 	ndev->cntl_sta = reg;
 
-	rc = pci_read_config_dword(ndev->ntb.pdev,
-				   AMD_LINK_STATUS_OFFSET, &stat);
-	if (rc)
+	if (ndev->ntb.topo == NTB_TOPO_SEC) {
+		/* Locate the pointer to Downstream Switch for this device */
+		pci_swds = pci_upstream_bridge(ndev->ntb.pdev);
+		if (pci_swds) {
+			/*
+			 * Locate the pointer to Upstream Switch for
+			 * the Downstream Switch.
+			 */
+			pci_swus = pci_upstream_bridge(pci_swds);
+			if (pci_swus) {
+				rc = pcie_capability_read_dword(pci_swus,
+								PCI_EXP_LNKCTL,
+								&stat);
+				if (rc)
+					return 0;
+			} else {
+				return 0;
+			}
+		} else {
+			return 0;
+		}
+	} else if (ndev->ntb.topo == NTB_TOPO_PRI) {
+		/*
+		 * For NTB primary, we simply read the Link Status and control
+		 * register of the NTB device itself.
+		 */
+		pdev = ndev->ntb.pdev;
+		rc = pcie_capability_read_dword(pdev, PCI_EXP_LNKCTL, &stat);
+		if (rc)
+			return 0;
+	} else {
+		/* Catch all for everything else */
 		return 0;
+	}
+
 	ndev->lnk_sta = stat;
 
 	return 1;
diff --git a/drivers/ntb/hw/amd/ntb_hw_amd.h b/drivers/ntb/hw/amd/ntb_hw_amd.h
index 139a307147bc..39e5d18e12ff 100644
--- a/drivers/ntb/hw/amd/ntb_hw_amd.h
+++ b/drivers/ntb/hw/amd/ntb_hw_amd.h
@@ -53,7 +53,6 @@
 #include <linux/pci.h>
 
 #define AMD_LINK_HB_TIMEOUT	msecs_to_jiffies(1000)
-#define AMD_LINK_STATUS_OFFSET	0x68
 #define NTB_LIN_STA_ACTIVE_BIT	0x00000002
 #define NTB_LNK_STA_SPEED_MASK	0x000F0000
 #define NTB_LNK_STA_WIDTH_MASK	0x03F00000
-- 
2.17.1