linux-kernel - [PATCH v2] watchdog: da9062: make restart handler atomic safe

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Date:   Wed, 15 Jan 2020 17:23:07 +0100
From:   Marco Felsch <m.felsch@...gutronix.de>
To:     support.opensource@...semi.com, linux@...ck-us.net,
        contact@...fanchrist.eu, Adam.Thomson.Opensource@...semi.com
Cc:     linux-watchdog@...r.kernel.org, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] watchdog: da9062: make restart handler atomic safe

The restart handler is executed during the shutdown phase which is
atomic/irq-less. The i2c framework supports atomic transfers since
commit 63b96983a5dd ("i2c: core: introduce callbacks for atomic
transfers") to address this use case. Using regmap within an atomic
context is allowed only if the regmap type is MMIO and the cache type
'flat' or no cache is used. Using the i2c_smbus_write_byte_data()
function can be done without additional tests because:
 1) the DA9062 is an i2c-only device and
 2) the i2c framework emulates the smbus protocol if the host adapter
    does not support smbus_xfer by using the master_xfer.

Signed-off-by: Marco Felsch <m.felsch@...gutronix.de>
---
Hi,

This patch is based on Stefan Lengfeld's RFC Patch [1].

[1] https://patchwork.ozlabs.org/patch/1085942/

Changes:

v2:
- adapt commit message
- add comment
- make use of i2c_smbus_write_byte_data()
---
 drivers/watchdog/da9062_wdt.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/watchdog/da9062_wdt.c b/drivers/watchdog/da9062_wdt.c
index c9b9d6394525..77b6b5336067 100644
--- a/drivers/watchdog/da9062_wdt.c
+++ b/drivers/watchdog/da9062_wdt.c
@@ -11,6 +11,7 @@
 #include <linux/platform_device.h>
 #include <linux/uaccess.h>
 #include <linux/slab.h>
+#include <linux/i2c.h>
 #include <linux/delay.h>
 #include <linux/jiffies.h>
 #include <linux/mfd/da9062/registers.h>
@@ -149,12 +150,13 @@ static int da9062_wdt_restart(struct watchdog_device *wdd, unsigned long action,
 			      void *data)
 {
 	struct da9062_watchdog *wdt = watchdog_get_drvdata(wdd);
+	struct i2c_client *client = to_i2c_client(wdt->hw->dev);
 	int ret;
 
-	ret = regmap_write(wdt->hw->regmap,
-			   DA9062AA_CONTROL_F,
-			   DA9062AA_SHUTDOWN_MASK);
-	if (ret)
+	/* Don't use regmap because it is not atomic safe */
+	ret = i2c_smbus_write_byte_data(client, DA9062AA_CONTROL_F,
+					DA9062AA_SHUTDOWN_MASK);
+	if (ret < 0)
 		dev_alert(wdt->hw->dev, "Failed to shutdown (err = %d)\n",
 			  ret);
 
-- 
2.20.1