[PATCH v9 08/13] PCI: Save and restore the ACS Control register

[sashiko-bot at kernel.org]

> Save the ACS Control register in pci_save_state() and write it back
> in pci_restore_state(), instead of recomputing the ACS controls from
> scratch with pci_enable_acs().
> 
> This makes ACS symmetric with the rest of a device's saved state. Today
> pci_save_state() ignores ACS entirely and pci_restore_state() re-enables
> the ACS controls from the kernel's current ACS policy. As a result, a
> device can come out of a reset with different ACS controls than it went
> in with, e.g. any controls programmed outside of pci_enable_acs() are
> silently dropped.
> 
> pci_enable_acs() runs when a driver binds to a device
> (pci_dma_configure()), i.e. after pci_bus_add_device() has already saved
> the device's state. Refresh the saved ACS Control register there as
> well, otherwise a subsequent reset would revert ACS back to the
> configuration left behind by firmware.
> 
> Devices that rely on device-specific quirks to enable an ACS equivalent
> keep that configuration outside of the ACS Control register, so keep
> configuring ACS from scratch for them. Do the same for devices that have
> no saved ACS state at all.
> 
> Reviewed-by: Bjorn Helgaas <bhelgaas at google.com>
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: David Matlack <dmatlack at google.com>

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

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Sashiko AI review · https://sashiko.dev/#/patchset/20260918200640.887030-1-dmatlack@google.com?part=8