PCI/ASPM: Disable L1 before disabling L1 PM Substates

PCI/ASPM: Disable L1 before disabling L1 PM Substates

PCIe r6.2, sec 5.5.4, requires that:

  If setting either or both of the enable bits for ASPM L1 PM Substates,
  both ports must be configured as described in this section while ASPM L1
  is disabled.

Previously, pcie_config_aspm_l1ss() assumed that "setting enable bits"
meant "setting them to 1", and it configured L1SS as follows:

  - Clear L1SS enable bits
  - Disable L1
  - Configure L1SS enable bits as required
  - Enable L1 if required

With this sequence, when disabling L1SS on an ARM A-core with a Synopsys
DesignWare PCIe core, the CPU occasionally hangs when reading
PCI_L1SS_CTL1, leading to a reboot when the CPU watchdog expires.

Move the L1 disable to the caller (pcie_config_aspm_link(), where L1 was
already enabled) so L1 is always disabled while updating the L1SS bits:

  - Disable L1
  - Clear L1SS enable bits
  - Configure L1SS enable bits as required
  - Enable L1 if required

Change pcie_aspm_cap_init() similarly.

Link: https://lore.kernel.org/r/20241007032917.872262-1-ajayagarwal@google.com
Signed-off-by: Ajay Agarwal <ajayagarwal@google.com>
[bhelgaas: comments, commit log, compute L1SS setting before config access]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>