From: cem <cem@FreeBSD.org>
Date: Tue, 13 Oct 2015 23:43:06 +0000 (+0000)
Subject: NTB: MFV 58b88920: Document HW errata
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=66946565079046433adc73a6528f8698c4eb249c;p=people%2Fjulieng%2Ffreebsd.git

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
---

diff --git a/sys/dev/ntb/ntb_hw/ntb_hw.c b/sys/dev/ntb/ntb_hw/ntb_hw.c
index 7f7fa5f82a8b..b45e8258f3c0 100644
--- a/sys/dev/ntb/ntb_hw/ntb_hw.c
+++ b/sys/dev/ntb/ntb_hw/ntb_hw.c
@@ -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))
 		/*