svn commit: r289274 - head/sys/dev/ntb/ntb_hw

[Conrad E. Meyer]

Author: cem
Date: Tue Oct 13 23:43:06 2015
New Revision: 289274
URL: https://svnweb.freebsd.org/changeset/base/289274

Log:
  NTB: MFV 58b88920: Document HW errata
  
  Add a comment describing the necessary ordering of modifications to the
  NTB Limit and Base registers.
  
  Authored by:	Jon Mason
  Obtained from:	Linux (Dual BSD/GPL driver)
  Sponsored by:	EMC / Isilon Storage Division

Modified:
  head/sys/dev/ntb/ntb_hw/ntb_hw.c

Modified: head/sys/dev/ntb/ntb_hw/ntb_hw.c
==============================================================================
--- head/sys/dev/ntb/ntb_hw/ntb_hw.c	Tue Oct 13 23:42:13 2015	(r289273)
+++ head/sys/dev/ntb/ntb_hw/ntb_hw.c	Tue Oct 13 23:43:06 2015	(r289274)
@@ -764,6 +764,11 @@ ntb_setup_xeon(struct ntb_softc *ntb)
 	 * which may hang the system.  To workaround this use the second memory
 	 * window to access the interrupt and scratch pad registers on the
 	 * remote system.
+	 *
+	 * There is another HW errata on the limit registers -- they can only
+	 * be written when the base register is (?)4GB aligned and < 32-bit.
+	 * This should already be the case based on the driver defaults, but
+	 * write the limit registers first just in case.
 	 */
 	if (HAS_FEATURE(NTB_REGS_THRU_MW))
 		/*