Re: [PATCH v3 1/2] PCI/PM: Keep the saved config space of an inaccessible device

[sashiko-bot@kernel.org]

> pci_save_state() saves the standard header without checking whether the
> device responded.  For an inaccessible device, each read returns all
> ones, overwriting the previous snapshot, which pci_restore_state()
> writes back after resume.  On a bridge, that sets every writable bit of
> the Bridge Control register, Secondary Bus Reset included, and sets the
> primary, secondary and subordinate bus numbers to 0xff, which cuts off
> everything below it.  This was seen on a MacBookPro14,3, where a bridge
> that stopped responding during system suspend came back after resume
> with bus numbers ff/ff/ff.
> 
> Commit e18d1abc3bff ("PCI: Avoid saving config space state if
> inaccessible") added pci_dev_config_accessible() and checks it before a
> reset.  Check it in pci_save_state() itself, so that system suspend is
> covered as well.
> 
> If it is not accessible, keep the previous snapshot, mark the state as
> saved and return 0.  This avoids changing callers or making the PM core
> warn about a low-power device without saved state.  pci_bus_add_device()
> saves the state when the device is added, so normally a snapshot exists.
> That snapshot can be older than the last values the device had, for
> example if its driver changed the Command register after the last
> successful save.
> 
> Assisted-by: LLM
> Signed-off-by: Francisco Beltrán Millalén <fbeltranmillalen@gmail.com>

Sashiko has reviewed this patch and found no issues.

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