Re: [Xen-devel] [PATCH FOR-4.5] xen: arm: Do not enable EFI in dom0 since it is not yet supported.

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 10/14/2014 02:47 PM, Ian Campbell wrote:
> On Tue, 2014-10-14 at 14:18 +0100, Julien Grall wrote:
>> On 10/14/2014 02:07 PM, Ian Campbell wrote:
>>> On Tue, 2014-10-14 at 13:58 +0100, Julien Grall wrote:
>>>> On 10/14/2014 01:49 PM, Ian Campbell wrote:
>>>>> On Tue, 2014-10-14 at 13:28 +0100, Julien Grall wrote:
>>>>>> Hi Ian,
>>>>>> 
>>>>>> On 10/14/2014 08:21 AM, Ian Campbell wrote:
>>>>>>> On Mon, 2014-10-13 at 12:37 -0700, Roy Franz wrote:
>>>>>>>> On Mon, Oct 13, 2014 at 9:20 AM, Julien Grall
>>>>>>>> <julien.grall@xxxxxxxxxx> wrote:
>>>>>>>>> (CC vijay)
>>>>>>>>> 
>>>>>>>>> Hi Suravee,
>>>>>>>>> 
>>>>>>>>> On 10/13/2014 05:17 PM, suravee.suthikulpanit@xxxxxxx
>>>>>>>>> wrote:
>>>>>>>>>> From: Suravee Suthikulpanit
>>>>>>>>>> <Suravee.Suthikulpanit@xxxxxxx>
>>>>>>>>>> 
>>>>>>>>>> Since EFI is not yet supported in dom0, we need to
>>>>>>>>>> remove the following properties from the chosen
>>>>>>>>>> node:
>>>>>>>>>> 
>>>>>>>>>> * linux,uefi-mmap-start * linux,uefi-mmap-size *
>>>>>>>>>> linux,uefi-mmap-desc-size *
>>>>>>>>>> linux,uefi-mmap-desc-ver
>>>>>>>>>> 
>>>>>>>>>> These are added by "arch/arm/efi/efi-boot.h:
>>>>>>>>>> fdt_add_uefi_nodes()", and used by dom0 kernel to
>>>>>>>>>> enable EFI.
>>>>>>>>>> 
>>>>>>>>>> Cc: Julien Grall <julien.grall@xxxxxxxxxx> Cc:
>>>>>>>>>> Stefano Stabellini
>>>>>>>>>> <stefano.stabellini@xxxxxxxxxxxxx> Cc: Ian Campbell
>>>>>>>>>> <ian.campbell@xxxxxxxxxx> Cc: Roy Franz
>>>>>>>>>> <roy.franz@xxxxxxxxxx> Signed-off-by: Suravee
>>>>>>>>>> Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
>>>>>>>>> 
>>>>>>>>> Reviewed-by: Julien Grall <julien.grall@xxxxxxxxxx>
>>>>>>>> 
>>>>>>>> Reviewed-by: Roy Franz <roy.franz@xxxxxxxxxx>
>>>>>>> 
>>>>>>> Acked-by: Ian Campbell <ian.campbell@.citrix.com>
>>>>>>> 
>>>>>>> But I do wonder why we don't just drop the hos /chosen
>>>>>>> node -- I think everything which should be in there is
>>>>>>> fabricated by the h/visor anyway.
>>>>>> 
>>>>>> I though about the same things yesterday, but the /chosen
>>>>>> node may contain other properties (such as OS specific)
>>>>>> that we may need to pass to DOM0.
>>>>> 
>>>>> What sort of thing are you thinking of here?
>>>> 
>>>> FreeBSD provides two properties (stdin and stdout) to choose
>>>> the input and the output methods.
>>>> 
>>>> Those properties need to be copied in DOM0 DT to allow the user
>>>> chose which console he wants to use (think about a platform
>>>> with 2 serial ports).
>>> 
>>> How do you know whether stdin/stdout were intended to apply to
>>> dom0 or Xen?
>> 
>> We specify the console for Xen via the Xen command line.
>> 
>>> What if dom0 wants to use hvc0? How is that expressed?
>> 
>> For now it has the priority against anything else. But in ideal
>> world, the HVC console should be describe in a device node add by
>> Xen.
>> 
>>> It seems to me that if bootargs is being consumed by Xen then 
>>> stdin/stdout ought to be consumed by Xen for consistency.
>> 
>> stdin/stdout is part of FreeBSD command line. If we use those 
>> properties, why don't we parse Linux command line to get the
>> console?
>> 
> 
> OK. I'm confused. I was talking about device-tree properties under
> /chosen so I thought you were saying that stdin/stdout were such 
> things. If they are part of the bsd command line (i.e. part of 
> xen,dom0-bootargs or similar) then there is no problem -- we pass
> them through just like we do today.
> 
>>> Which points to special handling for stdin/stdout in Xen, i.e. a 
>>> continuation of the whitelisting approach.
>> 
>> And how do you chose the console for DOM0? For Linux we have to
>> use console=hvc0 on the command line. FreeBSD choose to use
>> stdin/stdout.
> 
> Are you now saying that they aren't in the FreeBSD command line but
> are properties?
> 
> If you are saying that they are dt properties then stdin/stdout
> should be handled just like bootargs IMHO, not simply happen to work
> due to a partial blacklist

Yes they are properties of the device tree. We can't really interpret in
Xen because they are only meaningful for FreeBSD.

On Linux, the console is chosen via the command line. It happens that we
need to clearly specify "hvc" on it to be able to use the Xen console.

As said earlier, if we consume in Xen how do you choose the console for
FreeBSD? Those properties can be considered as the part of the FreeBSD
"command line".

Anyway, the stdin/stdout properties may not be the best examples.
Grepping the Documentation in Linux I have found those properties which
live in /chosen:
        - linux,pci-probe-only
        - linux,sysrq-reset-seq (actually it's a node)

The blacklist way is the best solution to make sure any newer kernel
will work (most of the time) out of box on Linux.

Regards,

-- 
Julien Grall

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