linux-kernel - Re: [PATCH 3/3] watchdog: xilinx: Add WDIOC

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Date:	Thu, 30 May 2013 07:21:45 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Michal Simek <monstr@...str.eu>
Cc:	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, Wim Van Sebroeck <wim@...ana.be>,
	linux-watchdog@...r.kernel.org
Subject: Re: [PATCH 3/3] watchdog: xilinx: Add WDIOC_SETTIMEOUT ioctl function

On Thu, May 30, 2013 at 04:15:45PM +0200, Michal Simek wrote:
> On 05/30/2013 04:07 PM, Guenter Roeck wrote:
> > On Thu, May 30, 2013 at 02:26:04PM +0200, Michal Simek wrote:
> >> Standard watchdog programs try to setup timeout
> >> via ioctl and this functionality should be implemented.
> >> Timeout value is hardcoded in the hardware but
> >> based on Documentation/watchdog/watchdog-api.txt
> >> can return the real timeout used in the same variable.
> >>
> >> Signed-off-by: Michal Simek <michal.simek@...inx.com>
> >> ---
> >>  drivers/watchdog/of_xilinx_wdt.c | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/drivers/watchdog/of_xilinx_wdt.c b/drivers/watchdog/of_xilinx_wdt.c
> >> index 79f358c..a3bbe72 100644
> >> --- a/drivers/watchdog/of_xilinx_wdt.c
> >> +++ b/drivers/watchdog/of_xilinx_wdt.c
> >> @@ -253,6 +253,7 @@ static long xwdt_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> >>  		xwdt_keepalive();
> >>  		return 0;
> >>
> >> +	case WDIOC_SETTIMEOUT:
> >>  	case WDIOC_GETTIMEOUT:
> >>  		if (no_timeout)
> >>  			return -ENOTTY;
> > 
> > Watchdog programs should check ident.options before trying to set the timeout.
> > If they don't, there is an application bug. I don't think it is a good idea
> > to start hacking the kernel to work around application bugs.
> 
> Based on Documentation/watchdog/watchdog-api.txt
> 
> "For some drivers it is possible to modify the watchdog timeout on the
> fly with the SETTIMEOUT ioctl, those drivers have the WDIOF_SETTIMEOUT
> flag set in their option field.  The argument is an integer

Yes, but WDIOF_SETTIMEOUT is not set in the driver's option field.

Guenter

> representing the timeout in seconds.  The driver returns the real
> timeout used in the same variable, and this timeout might differ from
> the requested one due to limitation of the hardware.
> 
>     int timeout = 45;
>     ioctl(fd, WDIOC_SETTIMEOUT, &timeout);
>     printf("The timeout was set to %d seconds\n", timeout);
> 
> This example might actually print "The timeout was set to 60 seconds"
> if the device has a granularity of minutes for its timeout."
> 
> should be completely fine that user application is trying to setup timeout
> and driver should return value based on it.
> 
> And yes, user application should check return value from ioctl call
> but still based on documentation driver can properly support it too.
> 
> Thanks,
> Michal
> 
> -- 
> Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
> w: www.monstr.eu p: +42-0-721842854
> Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
> Maintainer of Linux kernel - Xilinx Zynq ARM architecture
> Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform
> 
> 


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