linux-kernel - [PATCH 3.16 292/294] e1000e: fix call to do

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Message-ID: <lsq.1510009382.153420453@decadent.org.uk>
Date:   Mon, 06 Nov 2017 23:03:02 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Aaron Brown" <aaron.f.brown@...el.com>,
        "Jeff Kirsher" <jeffrey.t.kirsher@...el.com>,
        "Arnd Bergmann" <arnd@...db.de>,
        "Yanir Lubetkin" <yanirx.lubetkin@...el.com>,
        "Yanjiang Jin" <yanjiang.jin@...driver.com>
Subject: [PATCH 3.16 292/294] e1000e: fix call to do_div() to use u64 arg

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>

commit 30544af5483755b11bb5924736e9e0b45ef0644a upstream.

We were using s64 for lat_ns (latency nano-second value) since in
our calculations a negative value could be a resultant.  For negative
values, we then assign lat_ns to be zero, so the value passed to
do_div() was never negative, but do_div() expects the argument type
to be u64, so do a cast to resolve a compile warning seen on
PowerPC.

CC: Yanjiang Jin <yanjiang.jin@...driver.com>
CC: Yanir Lubetkin <yanirx.lubetkin@...el.com>
Reported-by: Yanjiang Jin <yanjiang.jin@...driver.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Tested-by: Aaron Brown <aaron.f.brown@...el.com>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/ethernet/intel/e1000e/ich8lan.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

--- a/drivers/net/ethernet/intel/e1000e/ich8lan.c
+++ b/drivers/net/ethernet/intel/e1000e/ich8lan.c
@@ -984,7 +984,7 @@ static s32 e1000_platform_pm_pch_lpt(str
 		u16 max_snoop, max_nosnoop;
 		u16 max_ltr_enc;	/* max LTR latency encoded */
 		s64 lat_ns;	/* latency (ns) */
-		s64 value;
+		u64 value;
 		u32 rxa;
 
 		if (!hw->adapter->max_frame_size) {
@@ -1011,12 +1011,13 @@ static s32 e1000_platform_pm_pch_lpt(str
 		 */
 		lat_ns = ((s64)rxa * 1024 -
 			  (2 * (s64)hw->adapter->max_frame_size)) * 8 * 1000;
-		if (lat_ns < 0)
-			lat_ns = 0;
-		else
-			do_div(lat_ns, speed);
+		if (lat_ns < 0) {
+			value = 0;
+		} else {
+			value = lat_ns;
+			do_div(value, speed);
+		}
 
-		value = lat_ns;
 		while (value > PCI_LTR_VALUE_MASK) {
 			scale++;
 			value = DIV_ROUND_UP(value, (1 << 5));