NTB: Xeon Doorbell errata workaround

Modifications to the 14th bit of the B2BDOORBELL register will not be
mirrored to the remote system due to a hardware issue.  To get around
the issue, shrink the number of available doorbell bits by 1.  The max
number of doorbells was being used as a way to referencing the Link
Doorbell bit.  Since this would no longer work, the driver must now
explicitly reference that bit.

This does not affect the xeon_errata_workaround case, as it is not using
the b2bdoorbell register.

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

2 files changed, 16 insertions, 5 deletions

diff --git a/drivers/ntb/ntb_hw.c b/drivers/ntb/ntb_hw.c
index 1cb6e51e6bda..6c9d73348735 100644
--- a/drivers/ntb/ntb_hw.c
+++ b/drivers/ntb/ntb_hw.c
@@ -678,6 +678,7 @@ static int ntb_xeon_setup(struct ntb_device *ndev)
                                 return -EINVAL;
 
                         ndev->limits.max_mw = SNB_ERRATA_MAX_MW;
+                        ndev->limits.max_db_bits = SNB_MAX_DB_BITS;
                         ndev->reg_ofs.spad_write = ndev->mw[1].vbase +
                                                    SNB_SPAD_OFFSET;
                         ndev->reg_ofs.rdb = ndev->mw[1].vbase +
@@ -690,6 +691,13 @@ static int ntb_xeon_setup(struct ntb_device *ndev)
                                SNB_PBAR4LMT_OFFSET);
                 } else {
                         ndev->limits.max_mw = SNB_MAX_MW;
+
+                        /* HW Errata on bit 14 of b2bdoorbell register.  Writes
+                         * will not be mirrored to the remote system.  Shrink
+                         * the number of bits by one, since bit 14 is the last
+                         * bit.
+                         */
+                        ndev->limits.max_db_bits = SNB_MAX_DB_BITS - 1;
                         ndev->reg_ofs.spad_write = ndev->reg_base +
                                                    SNB_B2B_SPAD_OFFSET;
                         ndev->reg_ofs.rdb = ndev->reg_base +
@@ -769,6 +777,7 @@ static int ntb_xeon_setup(struct ntb_device *ndev)
                  * have an equal amount.
                  */
                 ndev->limits.max_spads = SNB_MAX_COMPAT_SPADS / 2;
+                ndev->limits.max_db_bits = SNB_MAX_DB_BITS;
                 /* Note: The SDOORBELL is the cause of the errata.  You REALLY
                  * don't want to touch it.
                  */
@@ -793,6 +802,7 @@ static int ntb_xeon_setup(struct ntb_device *ndev)
                  * have an equal amount.
                  */
                 ndev->limits.max_spads = SNB_MAX_COMPAT_SPADS / 2;
+                ndev->limits.max_db_bits = SNB_MAX_DB_BITS;
                 ndev->reg_ofs.rdb = ndev->reg_base + SNB_PDOORBELL_OFFSET;
                 ndev->reg_ofs.ldb = ndev->reg_base + SNB_SDOORBELL_OFFSET;
                 ndev->reg_ofs.ldb_mask = ndev->reg_base + SNB_SDBMSK_OFFSET;
@@ -819,7 +829,6 @@ static int ntb_xeon_setup(struct ntb_device *ndev)
         ndev->reg_ofs.lnk_stat = ndev->reg_base + SNB_SLINK_STATUS_OFFSET;
         ndev->reg_ofs.spci_cmd = ndev->reg_base + SNB_PCICMD_OFFSET;
 
-        ndev->limits.max_db_bits = SNB_MAX_DB_BITS;
         ndev->limits.msix_cnt = SNB_MSIX_CNT;
         ndev->bits_per_vector = SNB_DB_BITS_PER_VEC;
 
@@ -986,7 +995,7 @@ static irqreturn_t xeon_event_msix_irq(int irq, void *dev)
                 dev_err(&ndev->pdev->dev, "Error determining link status\n");
 
         /* bit 15 is always the link bit */
-        writew(1 << ndev->limits.max_db_bits, ndev->reg_ofs.ldb);
+        writew(1 << SNB_LINK_DB, ndev->reg_ofs.ldb);
 
         return IRQ_HANDLED;
 }
@@ -1176,9 +1185,10 @@ static int ntb_setup_interrupts(struct ntb_device *ndev)
          */
         if (ndev->hw_type == BWD_HW)
                 writeq(~0, ndev->reg_ofs.ldb_mask);
-        else
-                writew(~(1 << ndev->limits.max_db_bits),
-                       ndev->reg_ofs.ldb_mask);
+        else {
+                u16 var = 1 << SNB_LINK_DB;
+                writew(~var, ndev->reg_ofs.ldb_mask);
+        }
 
         rc = ntb_setup_msix(ndev);
         if (!rc)
diff --git a/drivers/ntb/ntb_regs.h b/drivers/ntb/ntb_regs.h
index aa4bdd393c58..5381b65a6f3a 100644
--- a/drivers/ntb/ntb_regs.h
+++ b/drivers/ntb/ntb_regs.h
@@ -55,6 +55,7 @@
 #define SNB_MAX_COMPAT_SPADS    16
 /* Reserve the uppermost bit for link interrupt */
 #define SNB_MAX_DB_BITS         15
+#define SNB_LINK_DB             15
 #define SNB_DB_BITS_PER_VEC     5
 #define SNB_MAX_MW              2
 #define SNB_ERRATA_MAX_MW       1