NTB: Document HW errata
Add a comment describing the necessary ordering of modifications to the
NTB Limit and Base registers.
Signed-off-by: Jon Mason <jon.mason@intel.com>
diff --git a/drivers/ntb/ntb_hw.c b/drivers/ntb/ntb_hw.c
index fa97948..391c377 100644
--- a/drivers/ntb/ntb_hw.c
+++ b/drivers/ntb/ntb_hw.c
@@ -689,6 +689,12 @@
*/
writeq(ndev->mw[1].bar_sz + 0x1000, ndev->reg_base +
SNB_PBAR4LMT_OFFSET);
+ /* HW errata on the Limit registers. They can only be
+ * written when the base register is 4GB aligned and
+ * < 32bit. This should already be the case based on the
+ * driver defaults, but write the Limit registers first
+ * just in case.
+ */
} else {
ndev->limits.max_mw = SNB_MAX_MW;
@@ -707,6 +713,12 @@
* something silly
*/
writeq(0, ndev->reg_base + SNB_PBAR4LMT_OFFSET);
+ /* HW errata on the Limit registers. They can only be
+ * written when the base register is 4GB aligned and
+ * < 32bit. This should already be the case based on the
+ * driver defaults, but write the Limit registers first
+ * just in case.
+ */
}
/* The Xeon errata workaround requires setting SBAR Base