Re: [PATCH v2 3/3] PCI: Do not mistake an absent device for an active link

[sashiko-bot@kernel.org]

> When a bridge is no longer accessible, its Link Status register reads
> as 0xffff, which has both PCI_EXP_LNKSTA_DLLLA and PCI_EXP_LNKSTA_LT
> set.  The code that waits for the link then takes a dead link for an
> active one:
> 
>   - pci_bridge_wait_for_secondary_bus(), for ports up to 5 GT/s, decides
>     that the link is up and waits PCIE_RESET_READY_POLL_MS for the device
>     below it;
> 
>   - pcie_wait_for_link_status(), used for faster ports and by
>     pcie_retrain_link(), reports success at once when waiting for an
>     active link, and times out after PCIE_LINK_RETRAIN_TIMEOUT_MS when
>     waiting for LT to clear.
> 
> Treat an all-ones read as the device being gone.  All callers of
> pcie_wait_for_link_status() and pcie_retrain_link() treat any non-zero
> return as failure.
> 
> On a MacBookPro14,3 whose Thunderbolt controller does not come back from
> S3, the downstream ports of the controller are 2.5 GT/s ports that no
> longer answer.  Resume spent about 65 seconds waiting for the xHCI
> controller behind one of them ("not ready 65535ms after resume"); with
> the pci_bridge_wait_for_secondary_bus() change it gives up on that
> controller after about one second.  That machine never reaches
> pcie_wait_for_link_status() in this situation, so that part has not been
> tested.
> 
> Assisted-by: LLM
> Signed-off-by: Francisco Beltrán Millalén <fbeltranmillalen@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260930141914.6678-1-fbeltranmillalen@gmail.com?part=3