Re: [Qemu-devel] [PATCH] vfio: fix duplicate function call

[Cao jin <caoj.fnst@cn.fujitsu.com>]

On 10/14/2016 11:50 PM, Alex Williamson wrote:
> On Fri, 14 Oct 2016 19:16:59 +0800
> Cao jin <caoj.fnst@cn.fujitsu.com> wrote:
>
>> When vfio device is reset(encounter FLR, or bus reset), if need to do
>> bus reset(vfio_pci_hot_reset_one is called), vfio_pci_pre_reset &
>> vfio_pci_post_reset will be called twice.
>>
>> Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
>> ---
>> Also has a little question on vfio_pci_reset. it will be called when encounter
>> bus reset, or FLR. The reset method's priority in this function now is:
>>
>>      1. If has "device specific reset function", then do it
>>      2. If has FLR, then do it.
>>      3. If it can do bus reset(only 1 affected device), then do it
>>      4. If has pm_reset, then do it
>>
>> The question is: why pm reset has low priority than bus reset(if it does
>> can do a bus reset)? why bus reset is not the last choice? In PCI driver
>> of kernel, pls see __pci_dev_reset, we can see, if device support pm reset,
>> it won't do bus reset.
>
> The PCI spec doesn't really define what sort of reset is done with a PM
> reset.  My thinking was that if a device advertises an FLR capability
> then the hardware has made a concerted effort to have a per function
> reset mechanism available.  NoSoftRst- is not terribly common and it's
> not entirely clear to me that the hardware has made a conscious effort
> to provide this for the purposes of per function reset mechanism.
> Therefore I've opt'd to prioritize a bus reset over a PM reset.
>

I see, thanks for your infomation.

-- 
Yours Sincerely,

Cao jin