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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <AM6PR10MB2263127E716960B24D26DE76800F0@AM6PR10MB2263.EURPRD10.PROD.OUTLOOK.COM>
Date:   Thu, 23 Jan 2020 15:03:43 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     Marco Felsch <m.felsch@...gutronix.de>,
        Support Opensource <Support.Opensource@...semi.com>,
        "linux@...ck-us.net" <linux@...ck-us.net>,
        "contact@...fanchrist.eu" <contact@...fanchrist.eu>,
        Adam Thomson <Adam.Thomson.Opensource@...semi.com>
CC:     "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] watchdog: da9062: make restart handler atomic safe

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

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

> ---
> 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