Re: [PATCH v7 5/8] Watchdog: introduce ARM SBSA watchdog driver

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 




On Thu, Sep 10, 2015 at 06:29:53PM -0400, Jon Masters wrote:
> On 08/24/2015 01:01 PM, fu.wei@xxxxxxxxxx wrote:
> 
> > +	/*
> > +	 * Get the frequency of system counter from the cp15 interface of ARM
> > +	 * Generic timer. We don't need to check it, because if it returns "0",
> > +	 * system would panic in very early stage.
> > +	 */
> > +	gwdt->clk = arch_timer_get_cntfrq();
> 
> Just thinking out loud...
> 
> What happens later if we virtualize this device within KVM/QEMU/Xen and
> then live migrate to another system in which the frequency changes?
> 
I don't know, but I would suspect that we might end up in all kinds of
trouble if clocks can change like that, and not just in this driver.
Many drivers make the assumption that clock rates are not changed
under the hood. If it can happen, shouldn't there be a callback into
the drivers using the affected clock(s) ?

Also, it seems to me that changing a clock like that would be inherently
unsafe. For example, what will happen if the system is stopped and migrated
right after the clock frequency is read, but before the returned value
is used ? Can that happen ? Or does it only happen during suspend/resume
cycles, if it happens ?

Thanks,
Guenter
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Device Tree Compilter]     [Device Tree Spec]     [Linux Driver Backports]     [Video for Linux]     [Linux USB Devel]     [Linux PCI Devel]     [Linux Audio Users]     [Linux Kernel]     [Linux SCSI]     [XFree86]     [Yosemite Backpacking]
  Powered by Linux