Re: [Xen-devel] [PATCH] Improve the current FLR logic

[Yuji Shimada <shimada-yxb@xxxxxxxxxxxxxxx>]

Hi, Neo,

On Tue, 30 Sep 2008 23:53:22 -0700
"Neo Jia" <neojia@xxxxxxxxx> wrote:

> Yuji,
> 
> Could you show me how to use the hotplug method to restore the
> register?

Following code will help you to know how to use the hotplug
method(_HPP/_HPX method).

linux-2.6.18-xen.hg/drivers/pci/hotplug/pciehp_pci.c:program_fw_provided_values

Note: using the hotplug method is alternative approach to reconfigure
device after reset, without saving/restoring.


> Also, in the current implementation, we just read 4 bytes
> each time and write them from 0 to 256 - 4. Will this cause any side
> effect?

I'm not sure this cause any side effect.

But there is a case where memory enable bit is set to 1, while base
address registers are not programmed. Some devices might be confused.


Rich saving/restoring logic or using the hotplug method are needed for
following reasons.

- Most of the registers should not be restored, because there is a case
  where guest software programs configuration registers to invalid value.

- We need to program FW provided value to some registers to use
  machine's RAS function. For example, if system support SERR, SERR
  enable bit should be set to 1, so that device reports error.

Thanks,
--
Yuji Shimada


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