Re: [Xen-devel] [PATCH] arm/acpi: hide watchdog timer in GTDT table for dom0

[Julien Grall <julien.grall@xxxxxxx>]

On 30/11/16 14:43, Shanker Donthineni wrote:
> Hi Julien,
Hi Shanker,

> On 11/30/2016 08:31 AM, Shanker Donthineni wrote:
> > On 11/30/2016 04:29 AM, Julien Grall wrote:
> > > Hi Shanker,
> > >
> > > On 29/11/2016 02:59, Shanker Donthineni wrote:
> > > > Either we have to hide the watchdog timer section in GTDT or emulate
> > > > watchdog timer block for dom0. Otherwise, system gets panic when
> > > > dom0 accesses its MMIO registers. The current XEN doesn't support
> > > > virtualization of watchdog timer, so hide the watchdog timer section
> > > > for dom0.
> > > IHMO, the patch description is not really accurate. You are removing
> > > the platform timer array that contains watchdog but also Block Timer.
> > >
> > > Whilst you mention watchdog, you don't have a word on the Block Timer.
> > Sure, I'll include detailed description that has word  'Block Timer'
> > in v2 patch.
> >
> > > Taking a step back, DOM0 is not able to use it because it does not
> > > request to map the memory region (this is the behavior expected for
> > > PCI and AMBA devices). So this is a bug in the kernel for me.
> > Not all the drivers/modules in the Linux kernel are bounded to a device
> > object 'struct device'.  The watchdog timer driver is one of this
> > category, neither a PCIe nor a AMBA device.
> >
> > You can find GTDT watchdog timer code at
> > https://lkml.org/lkml/2016/7/25/34.
> Sorry, right link is https://lkml.org/lkml/2016/7/25/345
Thank you. Looking at patch #9 [1] that add the watchdog driver. A new 
platform device is created (see the call to 
platform_device_register_simple).
We already have a platform bus notifier for Xen in linux (see 
drivers/xen/arm-device.c). So I am not sure to understand what is the 
problem here as the region should be mapped by the notifier. Could you 
give a bit more details?
Regards,

[1] https://lkml.org/lkml/2016/7/25/353

--
Julien Grall

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