PCI: aardvark: Fix support for PME requester on emulated bridge

PCI: aardvark: Fix support for PME requester on emulated bridge

Enable aardvark PME interrupt unconditionally by unmasking it and read PME
requester ID to emulated bridge config space immediately after receiving
interrupt.

PME requester ID is stored in the PCIE_MSG_LOG_REG register, which contains
the last inbound message. So when new inbound message is received by HW
(including non-PM), the content in PCIE_MSG_LOG_REG register is replaced by
a new value.

PCIe specification mandates that subsequent PMEs are kept pending until the
PME Status Register bit is cleared by software by writing a 1b.

Support for masking/unmasking PME interrupt on emulated bridge via
PCI_EXP_RTCTL_PMEIE bit is now implemented only in emulated bridge config
space, to ensure that we do not miss any aardvark PME interrupt.

Reading of PCI_EXP_RTCAP and PCI_EXP_RTSTA registers is simplified as final
value is now always stored into emulated bridge config space by the
interrupt handler, so there is no need to implement support for these
registers in read_pcie callback.

Clearing of W1C bit PCI_EXP_RTSTA_PME is now also simplified as it is done
by pci-bridge-emul.c code for emulated bridge config space. So there is no
need to implement support for clearing this bit in write_pcie callback.

Link: https://lore.kernel.org/r/20220110015018.26359-18-kabel@kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>