linux-imx

PCI: designware: Exchange viewport of `MEMORYs' and `CFGs/IOs'

When we have only two view ports in a DesignWare PCIe platform, iatu0
is used for both CFG and IO accesses.  When CFGs are sent to peripherals
(e.g., lspci), iatu0 frequently switches between CFG and IO.

For such scenarios, a MEMORY might be sent as an IOs by mistake.
Considering the following configurations:

  MEMORY  ->   BASE_ADDR: 0xb4100000, LIMIT: 0xb4100FFF, TYPE=mem
  CFG     ->   BASE_ADDR: 0xb4000000, LIMIT: 0xb4000FFF, TYPE=cfg
  IO      ->   BASE_ADDR: 0xFFFFFFFF, LIMIT: 0xFFFFFFFE, TYPE=io

Suppose PCIe has just completed a CFG access.  To switch back to IO, it
sets the BASE_ADDR to 0xFFFFFFFF, LIMIT 0xFFFFFFFE and TYPE to IO.  When
another CFG comes, the BASE_ADDR is set to 0xb4000000 to switch to CFG.  At
this moment, a MEMORY access shows up, since it matches with iatu0 (due to
0xb4000000 <= MEMORY BASE_ADDR <= MEMORY LIMIT <= 0xFFFFFFF), it is treated
as an IO access by mistake, then sent to perpheral.

This patch fixes the problem by exchanging the assignments of `MEMORYs' and
`CFGs/IOs', which assigning MEMORYs to iatu0, CFGs and IOs to iatu1.

We can still have issues with IO transfer, however memory transfer is used
predominantly therefore we are just minimizing the risk of failure.
Actually, we can not do much when we have only two viewports.  We can
either not allow the less frequent IO transfers at all, or can live with a
remote possibility of getting it corrupted.

Signed-off-by: Dong Bo <dongbo4@huawei.com>
[pratyush.anand@gmail.com: Modified commit log to capture remote risk]
Signed-off-by: Pratyush Anand <pratyush.anand@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>