On Fri, Jan 05, 2018 at 02:26:34PM +0000, Bharat Kumar Gogada wrote: > 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 [1], linux kernel will hang for the above AXI responses. > As of now arm64 RAS is still work in progress [2]. > > [1] https://www.spinics.net/lists/arm-kernel/msg624203.html > > [2] https://patchwork.kernel.org/patch/9973967/ > > The check can be removed, if above issues were addressed. I do not see why the above "issues" should be addressed in order to remove that check - as it was pointed out in this thread it just does not solve anything, so what's the reason for keeping it ? Lorenzo
