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SubjectRe: [PATCH 2/2] PCI,pciehp: avoid add a device already exist during pciehp_resume
>> If the slot support surprise hot remove, this action maybe safe. right?
>
> If there's no device, config space accesses performed by .remove()
> will fail (reads will return -1 data or error; writes will be
> dropped). MMIO or I/O port accesses may fail with machine checks or
> similar bad things. But I don't see a way around that except by
> fixing drivers as we encounter issues like that.
>
> Since you're not changing anything here, I don't think we should worry
> about it for now.

OK.

>
>>>> remove the old card firstly, then add the new card.
>>>
>>> With your patch, I think we'll call the old driver's .remove() method
>>> on the new device. This seems bad; see below.
>>
>> Ah, this is issue.
>> What about power off slot first, then call the old driver's remove() method
>> will not touch the new physical device. After the old driver's remove() cleanup,
>> we call pciehp_enable_slot() to power on and enable the new device.
>
> Turning off power to the slot seems like a reasonable approach. Then
> we can run the old .remove() method in basically the same way we would
> in case 2.

Hmmm, I will follow this method to rework this patch in next version.

>
>>> With your patch, if we remove and reinsert the same device while
>>> suspended, we do nothing because the DSN didn't change. Previously we
>>> called pciehp_enable_slot(). I don't know if we need to do anything
>>> here or not.
>>
>> Mainly to avoid the redundant device add, the same like the changes for case 4
>
> I don't know whether it's redundant or not. Obviously if we remove
> and reinsert a device, we lose *all* state that was in the device. If
> we lose everything even if the card stayed inserted the whole time we
> were suspended, we must already deal with that and the "add" would be
> redundant. But if the state of the card is different if it got pulled
> and reinserted, the "add" would be necessary.

This is a key issue, sorry, I'm not familiar with PM :(
In my opinion, the device driver .suspend() method will be called
regardless of system enter in suspend to RAM(S3) or suspend to Disk(S4). Driver will
save the pci/pcie/pci-x state in .suspend() method. So once device driver .resume()
method be called, the pci/pcie/pci-x state willl be restored.
Because suspend to disk will power off whole system, so I thought if the device
was removed and inserted same device(DSN) again, maybe .resume will enable this device ok
regardless of the pci config space state has been changed.

If I have any thing above understanding wrong, please correct me, thanks!

>
>>>> 4. slot is non empty before suspend, no action during suspend.
>>>> We should do nothing in pciehp_resume, but we call
>>>> pciehp_enable_slot(), so some uncomfortable messages show like above.
>>>> In this case, we can improve it a little by add a guard
>>>> if (!list_empty(bus->devices)).
>>>
>>> This is the common case. Previously we called pciehp_enable_slot(),
>>> and with your patch we do nothing. I think that seems sensible, but
>>> this part should be split into a separate patch. That way we can keep
>>> the benefit of this change even if we trip over something with the
>>> other changes.
>>
>> OK, I will split this changes into a new patch.
>
> Actually, without your DSN changes, I don't think we can distinguish
> this from case 3. So I doubt it really could be split out.

I will try, but I think this is not a big deal :)

>
> .
>


--
Thanks!
Yijing



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