Re: [PATCH 1/1] pcie: Do not set power state for some hot-plugged devices

[Gerd Hoffmann]

On Thu, Dec 16, 2021 at 06:10:40PM -0500, Annie.li wrote:
> Hello Gerd,
> 
> On 12/16/2021 1:11 AM, Gerd Hoffmann wrote:
> > 
> > Looking again, the difference is probably the reset handling.
> > pcie_cap_slot_reset() will turn on power (via PCI_EXP_SLTCTL_PCC) in
> > case some device is plugged into the slot.
> If the VM is booting from the system disk in the qemu command line(no
> hot-plug),
> pcie_cap_slot_reset turns on the power for this device. And this happens
> before
> the VM runs into VM_STATE_PRELAUNCH state.(I add '-S' option in this case
> for comparison)
> > 
> > So I suspect when plugging devices during VM_STATE_PRELAUNCH they are
> > resetted individually (specifically before the device is plugged),
> When the device is hot-plugged in VM_STATE_PRELAUNCH state, there is no
> reset for the device during this state. Before entering this state,
> pcie_cap_slot_reset  does get called for the device(like general VM
> booting).
> However, it doesn't turn on the power. I think this is due to that the
> device isn't
> hot-plugged yet, and "populated" value is false.

Ok, so maybe we just need to move the device reset from "before
prelaunch" to "after prelaunch" ?

> > whereas otherwise they are resetted when all devices are plugged in.
> > 
> > Does resetting devices when leaving RUN_STATE_PRELAUNCH fix this?
> I suppose only calling pcie_cap_slot_reset  isn't sufficient? maybe
> rp_reset?

Well, the underlying problem I see here is that the setup workflow for
devices is different depending how they got added (cmd line vs.
prelauch).  This should not be the case.

I wouldn't be surprised if we find this causing similar issues in other
devices.

> Just thinking of the implementation, if the patch is deployed in this way,
> isn't the change is more complicated than the current one? :) Maybe I've
> missed something here.

I want the root cause be found and fixed, not band aid being applied ...

take care,
  Gerd