Why do we check for "link-up" in *_pcie_valid_device()?
Bharat Kumar Gogada
bharatku at xilinx.com
Fri Jan 5 06:26:34 PST 2018
On Fri, Dec 22, 2017 at 01:02:28PM +0000, Bharat Kumar Gogada wrote:
> Bjorn wrote:
>> In the PCI config access path, the *_pcie_valid_device() functions in
>> the dwc, altera, rockchip, and xilinx drivers all check whether the
>> link is up.
>> I think this is racy because the link may go down after we check but
>> before we perform the config access.
>> What would blow up if we removed the *_pcie_link_up() checks?
>> I'd like to either remove the checks or add comments about why the
>> race is acceptable. If we've covered this before, I apologize.
>> Adding a comment will keep me from pestering you about this again in
>> the future.
> In both Xilinx driver cases when link is down, hardware responds by
> AXI DECERR/SLVERR status which causes an exception, synchronous
> external abort to CPU. This causes system to hang, so we need this
> check for both of our drivers. We will add comments.
This is a problem, and checking whether the link is up is a workaround but not a real solution. That means your system may hang if the link happens to go down at the wrong time.
A real solution would be to handle the synchronous external abort so it doesn't cause a system hang.
Yes, I agree that this is workaround. For pcie-xilinx.c for arm32, we can have fault handling similar to "imx6q_pcie_abort_handler" in drivers/pci/dwc/pci-imx6.c.
Since this driver is same for Microblaze architecture also, it requires separate handling.
For pcie-xilinx-nwl.c ARM64 as per link , linux kernel will hang for the above AXI responses.
As of now arm64 RAS is still work in progress .
The check can be removed, if above issues were addressed.
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