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

[Julien Grall <julien.grall@arm.com>]

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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