Re: [PATCH] x86/PCI: Fully disable devices before releasing IRQ resource

From: Jiang Liu
Date: Wed Mar 11 2015 - 21:41:50 EST

On 2015/3/12 9:17, Rafael J. Wysocki wrote:
> On Wednesday, March 11, 2015 10:04:42 PM Luck, Tony wrote:
>>>> Unfortunately there's a long standing comment in pci_device_remove():
>>>> /*
>>>> * We would love to complain here if pci_dev->is_enabled is set, that
>>>> * the driver should have called pci_disable_device(), but the
>>>> * unfortunate fact is there are too many odd BIOS and bridge setups
>>>> * that don't like drivers doing that all of the time.
>>>> * Oh well, we can dream of sane hardware when we sleep, no matter how
>>>> * horrible the crap we have to deal with is when we are awake...
>>>> */
>>>> So, unless we can somehow ignore that comment, I suspect forcing the
>>>> device to be disabled on driver remove, whether done from pci-core or
>>>> from x86/pci, is going to cause all sorts of breakage. Are the
>>>> expectations set by b4b55cda5874 really valid? It seems like something
>>>> needs to be done to allow the IRQ to be automatically re-established on
>>>> x86 regardless of the driver doing the right thing when releasing the
>>>> device. We're still looking at a regression for v4.0 as a result of
>>>> b4b55cda5874.
>>> In which case we probably should revert commit b4b55cda5874 for the time being.
>>> At least I'd be very nervous about any ad-hoc fixes at this stage of the cycle.
>> The comment goes back to the dawn of "git" time ... not sure how much further
>> back.
>> Is this actually still an issue on modern systems? Maybe we need a black list
>> or white list to separate the good from bad systems?
> The answer to that is "We don't know" and in my not so humble opinion it is too
> risky to try to find out at the end of the cycle.
Hi Rafael and Alex,
How about a patch which:
1) gives a warning if PCI device is still enabled when unloading driver
2) release PCI interrupt only if PCI device is disabled.
By this way, we could support IOAPIC hot-removal on latest platforms and
avoid regressions on old platforms.

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