In case the controller is transitioning to L1 in rcar_pcie_config_access(),
any read/write access to PCIECDR triggers asynchronous external abort. This
is because the transition to L1 link state must be manually finished by the
driver. The PCIe IP can transition back from L1 state to L0 on its own.

The current asynchronous external abort hook implementation restarts
the instruction which finally triggered the fault, which can be a
different instruction than the read/write instruction which started
the faulting access. Usually the instruction which finally triggers
the fault is one which has some data dependency on the result of the
read/write. In case of read, the read value after fixup is undefined,
while a read value of faulting read should be PCI_ERROR_RESPONSE.

It is possible to enforce the fault using 'isb' instruction placed
right after the read/write instruction which started the faulting
access. Add custom register accessors which perform the read/write
followed immediately by 'isb'.

This way, the fault always happens on the 'isb' and in case of read,
which is located one instruction before the 'isb', it is now possible
to fix up the return value of the read in the asynchronous external
abort hook and make that read return PCI_ERROR_RESPONSE.

Link: https://lore.kernel.org/r/20220312212349.781799-2-marek.vasut@gmail.comTested-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NMarek Vasut <marek.vasut+renesas@gmail.com>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: NArnd Bergmann <arnd@arndb.de>
Reviewed-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Krzysztof Wilczyński <kw@linux.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Wolfram Sang <wsa@the-dreams.de>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: linux-renesas-soc@vger.kernel.org