Re: [PATCH] PCI: Update saved Max Payload Size in pcie_set_mps()

[Keith Busch <kbusch@kernel.org>]

On Mon, Oct 05, 2026 at 02:41:55PM +0200, Niklas Cassel wrote:
> pcie_set_mps() changes the Max Payload Size (MPS) in the Device Control
> register but leaves the copy saved by pci_save_state() alone, so the next
> pci_restore_state() puts back the old value.
> 
> The PCI core does change the MPS of devices whose state has already been
> saved: pci_configure_mps() reduces a Root Port's MPS when a device with a
> smaller MPS Supported is hot-added directly below it (commit 9f0e89359775
> ("PCI: Match Root Port's MPS to endpoint's MPSS as necessary")), and with
> "pci=pcie_bus_safe", pcie_bus_configure_settings() can do the same when
> pciehp calls it after a hot-add.  The Root Port's state was saved when it
> was added and again when portdrv probed it.
> 
> Since commit 3fc686d550f6 ("PCI/ERR: Add support for resetting the Root
> Ports in a platform-specific way"), pcibios_reset_secondary_bus() restores
> that saved state, without saving it first, after host->reset_root_port()
> has reset the Root Port, e.g. during AER recovery or on Link Down with the
> qcom and Rockchip DWC drivers.  The Root Port then goes back to the old,
> larger MPS while the device below it is restored to the smaller one, so
> the Root Port may send TLPs that the device treats as Malformed.
> 
> Update the saved copy of Device Control when pcie_set_mps() changes the
> MPS, like commit 909f7bf9b080 ("PCI: Update saved_config_space upon
> resource assignment") does for BARs.

Looks good to me:

Reviewed-by: Keith Busch <kbusch@kernel.org>