linux-kernel - [PATCH 3.16 49/87] can: flexcan: fix timeout when set small bitrate

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Message-ID: <lsq.1570043211.365040761@decadent.org.uk>
Date:   Wed, 02 Oct 2019 20:06:51 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Joakim Zhang" <qiangqing.zhang@....com>,
        "Dong Aisheng" <aisheng.dong@....com>,
        "Marc Kleine-Budde" <mkl@...gutronix.de>
Subject: [PATCH 3.16 49/87] can: flexcan: fix timeout when set small bitrate

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

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

From: Joakim Zhang <qiangqing.zhang@....com>

commit 247e5356a709eb49a0d95ff2a7f07dac05c8252c upstream.

Current we can meet timeout issue when setting a small bitrate like
10000 as follows on i.MX6UL EVK board (ipg clock = 66MHZ, per clock =
30MHZ):

| root@...6ul7d:~# ip link set can0 up type can bitrate 10000

A link change request failed with some changes committed already.
Interface can0 may have been left with an inconsistent configuration,
please check.

| RTNETLINK answers: Connection timed out

It is caused by calling of flexcan_chip_unfreeze() timeout.

Originally the code is using usleep_range(10, 20) for unfreeze
operation, but the patch (8badd65 can: flexcan: avoid calling
usleep_range from interrupt context) changed it into udelay(10) which is
only a half delay of before, there're also some other delay changes.

After double to FLEXCAN_TIMEOUT_US to 100 can fix the issue.

Meanwhile, Rasmus Villemoes reported that even with a timeout of 100,
flexcan_probe() fails on the MPC8309, which requires a value of at least
140 to work reliably. 250 works for everyone.

Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
Reviewed-by: Dong Aisheng <aisheng.dong@....com>
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/can/flexcan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/can/flexcan.c
+++ b/drivers/net/can/flexcan.c
@@ -157,7 +157,7 @@

 #define FLEXCAN_MB_CODE_MASK		(0xf0ffffff)

-#define FLEXCAN_TIMEOUT_US             (50)
+#define FLEXCAN_TIMEOUT_US		(250)

 /*
  * FLEXCAN hardware feature flags