Returning fabricated CRS value (0xFFFF0001) by PCIe Root Complex to OS is
allowed only for 4-byte PCI_VENDOR_ID config read request and only when
CRSSVE bit in Root Port PCIe device is enabled. In all other error PCIe
Root Complex must return all-ones.
So implement this logic in pci-aardvark.c driver properly.
aardvark HW does not have Root Port PCIe device and U-Boot does not
implement emulation of this device. So expect that CRSSVE bit is set as
U-Boot can already handle CRS value for PCI_VENDOR_ID config read request.
More callers of pci_bus_read_config() function in U-Boot do not check for
return value, but check readback value. Therefore always fill readback
value in pcie_advk_read_config() function. On error fill all-ones of
correct size as it is required for PCIe Root Complex.
And also correctly propagates error from failed config write request to
return value of pcie_advk_write_config() function. Most U-Boot callers
ignores this return value, but it is a good idea to return correct value
from function.
These issues about return value of failed config read requests, including
special handling of CRS were reported by Lorenzo and Bjorn for Linux kernel
driver pci-aardvark together with quotes from PCIe r4.0 spec, see details:
https://lore.kernel.org/linux-pci/20210624213345.3617-1-pali@kernel.org/t/#u
Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>
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