PCI/ASPM: Mask ASPM states based on Devicetree properties

Some platforms require selectively disabling specific ASPM states on a
given PCIe link to avoid link instability or functional failures caused by
board-level connectivity constraints such as PCB routing, connectors,
slots, or external cabling.

Devicetree supports disabling ASPM L0s, L1, and L1 PM Substates via the
'aspm-no-l0s', 'aspm-no-l1' [1], and 'aspm-no-l1ss' [2] properties.
However, the ASPM driver does not currently honor these properties when
initializing the default link state.

When firmware enables L1 PM Substates before the kernel takes over,
masking aspm_support alone is insufficient to disable them in hardware.
pcie_config_aspm_link() guards L1SS configuration behind a check on
aspm_capable, which is derived from aspm_support. Once aspm_support is
masked, pcie_config_aspm_l1ss() is never called, leaving
firmware-enabled L1SS substates active in hardware.

Fix this by introducing pcie_link_has_aspm_override() to check for DT
override properties on either endpoint of the link. In
pcie_aspm_override_default_link_state(), use it to:

  - Mask aspm_support, aspm_default, and aspm_enabled for any disabled
    state, so software's view of the link stays in sync with what is
    actually programmed in hardware. Leaving aspm_enabled stale would make
    pcie_aspm_enabled() and the aspm sysfs attributes report a state as
    active even after it has been masked, and could cause
    pcie_config_aspm_link()'s "already in requested state" check to skip
    reprogramming hardware to match.

  - Explicitly call pcie_config_aspm_l1ss(link, 0) before masking
    aspm_support when firmware has L1SS active and DT requests disabling L1
    or L1SS, since pcie_config_aspm_link() will no longer do so once
    aspm_capable is derived from the masked aspm_support.

Move the aspm_default initialization and
pcie_aspm_override_default_link_state() call in pcie_aspm_cap_init() to
before the "Restore L0s/L1" block. pcie_aspm_cap_init() disables L1 in
hardware prior to aspm_l1ss_init() and re-enables it only in the restore
block. Calling pcie_config_aspm_l1ss() while L1 is already disabled
satisfies its precondition ("Caller must disable L1 first"), whereas the
previous placement after the restore violated it.

Since the restore block writes back the parent_lnkctl/child_lnkctl snapshot
taken from hardware before the DT override ran, mask the L0s and L1 enable
bits out of that snapshot for any state the override has just disabled in
aspm_support. Otherwise the restore step would unconditionally reprogram
the link back to firmware's original L0s/L1 configuration, defeating the
Devicetree override it is meant to enforce.

Move pcie_config_aspm_l1ss() earlier in the file so it can be called
from pcie_aspm_override_default_link_state().

Link [1]: https://github.com/devicetree-org/dt-schema/pull/188
Link [2]: https://github.com/devicetree-org/dt-schema/pull/190

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20260727-aspm-v6-3-2ebb3ee7ef71@oss.qualcomm.com

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