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From:   Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
To:     Marco Felsch <m.felsch@pengutronix.de>,
        Support Opensource <Support.Opensource@diasemi.com>,
        "linux@roeck-us.net" <linux@roeck-us.net>,
        "contact@stefanchrist.eu" <contact@stefanchrist.eu>,
        Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
CC:     "linux-watchdog@vger.kernel.org" <linux-watchdog@vger.kernel.org>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v2] watchdog: da9062: make restart handler atomic safe
Thread-Topic: [PATCH v2] watchdog: da9062: make restart handler atomic safe
Thread-Index: AQHVy8AZrIm80Z5wI0Soa5b+stqPP6f4ZI7w
Date:   Thu, 23 Jan 2020 15:03:43 +0000
Message-ID: <AM6PR10MB2263127E716960B24D26DE76800F0@AM6PR10MB2263.EURPRD10.PROD.OUTLOOK.COM>
References: <20200115162307.7336-1-m.felsch@pengutronix.de>
In-Reply-To: <20200115162307.7336-1-m.felsch@pengutronix.de>
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On 15 January 2020 16:23, Marco Felsch wrote:

> 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.
>=20
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>

Reviewed-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>

> ---
> Hi,
>=20
> This patch is based on Stefan Lengfeld's RFC Patch [1].
>=20
> [1] https://patchwork.ozlabs.org/patch/1085942/
>=20
> Changes:
>=20
> 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(-)
>=20
> 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_devic=
e
> *wdd, unsigned long action,
>  			      void *data)
>  {
>  	struct da9062_watchdog *wdt =3D watchdog_get_drvdata(wdd);
> +	struct i2c_client *client =3D to_i2c_client(wdt->hw->dev);
>  	int ret;
>=20
> -	ret =3D regmap_write(wdt->hw->regmap,
> -			   DA9062AA_CONTROL_F,
> -			   DA9062AA_SHUTDOWN_MASK);
> -	if (ret)
> +	/* Don't use regmap because it is not atomic safe */
> +	ret =3D i2c_smbus_write_byte_data(client, DA9062AA_CONTROL_F,
> +					DA9062AA_SHUTDOWN_MASK);
> +	if (ret < 0)
>  		dev_alert(wdt->hw->dev, "Failed to shutdown (err =3D %d)\n",
>  			  ret);
>=20
> --
> 2.20.1