Re: [RFC][PATCH] pci-assign: Drop support for raw ioport access

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-05-28 16:06, Avi Kivity wrote:
> On 05/28/2012 04:03 PM, Jan Kiszka wrote:
>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>
>> If the kernel does not support ioport access via sysfs, passthrough can
>> only help if the unlikely case that a port <= 0x3ff is provided by the
>> device. So drop this to simplify the code and to allow dropping the
>> corresponding KVM infrastructure in preparation of upstream merge.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>> ---
>>
>> Does anyone recall the precise use case this was introduced for? It
>> exists since day #1, so commit logs do not help.
> 
> At a wild guess, graphics device assignment.

The only explanation now. But that requires more work anyway (e.g. to
claim the VGA adapter toward the kernel). And I but we would rather do
this on top of VFIO on day.

> 
> Under what conditions would the kernel not support ioport access via sysfs?
> 

No clue. The oldest kernel I checked (2.6.16) does not contain traces it
would refuse to provide access.

Jan

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