NTB: Xeon Errata Workaround

There is a Xeon hardware errata related to writes to SDOORBELL or
B2BDOORBELL in conjunction with inbound access to NTB MMIO Space, which
may hang the system.  To workaround this issue, use one of the memory
windows to access the interrupt and scratch pad registers on the remote
system.  This bypasses the issue, but removes one of the memory windows
from use by the transport.  This reduction of MWs necessitates adding
some logic to determine the number of available MWs.

Since some NTB usage methodologies may have unidirectional traffic, the
ability to disable the workaround via modparm has been added.

See BF113 in
http://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xeon-c5500-c3500-spec-update.pdf
See BT119 in
http://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xeon-e5-family-spec-update.pdf

Signed-off-by: Jon Mason <jon.mason@intel.com>

1 files changed, 33 insertions, 6 deletions

diff --git a/drivers/ntb/ntb_hw.h b/drivers/ntb/ntb_hw.h
index 6a4f56f..72fcb22 100644
--- a/drivers/ntb/ntb_hw.h
+++ b/drivers/ntb/ntb_hw.h
@@ -68,7 +68,7 @@
 
 #define NTB_HB_TIMEOUT		msecs_to_jiffies(1000)
 
-#define NTB_NUM_MW		2
+#define NTB_MAX_NUM_MW		2
 
 enum ntb_hw_event {
 	NTB_EVENT_SW_EVENT0 = 0,
@@ -96,11 +96,12 @@ struct ntb_device {
 	struct pci_dev *pdev;
 	struct msix_entry *msix_entries;
 	void __iomem *reg_base;
-	struct ntb_mw mw[NTB_NUM_MW];
+	struct ntb_mw mw[NTB_MAX_NUM_MW];
 	struct {
-		unsigned int max_spads;
-		unsigned int max_db_bits;
-		unsigned int msix_cnt;
+		unsigned char max_mw;
+		unsigned char max_spads;
+		unsigned char max_db_bits;
+		unsigned char msix_cnt;
 	} limits;
 	struct {
 		void __iomem *pdb;
@@ -132,6 +133,32 @@ struct ntb_device {
 };
 
 /**
+ * ntb_max_cbs() - return the max callbacks
+ * @ndev: pointer to ntb_device instance
+ *
+ * Given the ntb pointer, return the maximum number of callbacks
+ *
+ * RETURNS: the maximum number of callbacks
+ */
+static inline unsigned char ntb_max_cbs(struct ntb_device *ndev)
+{
+	return ndev->max_cbs;
+}
+
+/**
+ * ntb_max_mw() - return the max number of memory windows
+ * @ndev: pointer to ntb_device instance
+ *
+ * Given the ntb pointer, return the maximum number of memory windows
+ *
+ * RETURNS: the maximum number of memory windows
+ */
+static inline unsigned char ntb_max_mw(struct ntb_device *ndev)
+{
+	return ndev->limits.max_mw;
+}
+
+/**
  * ntb_hw_link_status() - return the hardware link status
  * @ndev: pointer to ntb_device instance
  *
@@ -148,7 +175,7 @@ static inline bool ntb_hw_link_status(struct ntb_device *ndev)
  * ntb_query_pdev() - return the pci_dev pointer
  * @ndev: pointer to ntb_device instance
  *
- * Given the ntb pointer return the pci_dev pointerfor the NTB hardware device
+ * Given the ntb pointer, return the pci_dev pointer for the NTB hardware device
  *
  * RETURNS: a pointer to the ntb pci_dev
  */