CVE-2024-43876: PCI: rcar: Demote WARN() to dev_warn_ratelimited() in rcar_pcie_wakeup()

In the Linux kernel, the following vulnerability has been resolved:

PCI: rcar: Demote WARN() to devwarnratelimited() in rcarpciewakeup()

Avoid large backtrace, it is sufficient to warn the user that there has been a link problem. Either the link has failed and the system is in need of maintenance, or the link continues to work and user has been informed. The message from the warning can be looked up in the sources.

This makes an actual link issue less verbose.

First of all, this controller has a limitation in that the controller driver has to assist the hardware with transition to L1 link state by writing L1IATN to PMCTRL register, the L1 and L0 link state switching is not fully automatic on this controller.

In case of an ASMedia ASM1062 PCIe SATA controller which does not support ASPM, on entry to suspend or during platform pmtest, the SATA controller enters D3hot state and the link enters L1 state. If the SATA controller wakes up before rcarpciewakeup() was called and returns to D0, the link returns to L0 before the controller driver even started its transition to L1 link state. At this point, the SATA controller did send an PMENTERL1 DLLP to the PCIe controller and the PCIe controller received it, and the PCIe controller did set PMSR PMEL1RX bit.

Once rcarpciewakeup() is called, if the link is already back in L0 state and PMEL1RX bit is set, the controller driver has no way to determine if it should perform the link transition to L1 state, or treat the link as if it is in L0 state. Currently the driver attempts to perform the transition to L1 link state unconditionally, which in this specific case fails with a PMSR L1FAEG poll timeout, however the link still works as it is already back in L0 state.

Reduce this warning verbosity. In case the link is really broken, the rcarpcieconfigaccess() would fail, otherwise it will succeed and any system with this controller and ASM1062 can suspend without generating a backtrace.