On Tue, Sep 29, 2020 at 5:5:41, Z.q. Hou <zhiqiang.hou@xxxxxxx> wrote: > Hi Lorenzo, > > Thanks a lot for your comments! > > > -----Original Message----- > > From: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> > > Sent: 2020年9月28日 17:39 > > To: Z.q. Hou <zhiqiang.hou@xxxxxxx> > > Cc: Rob Herring <robh@xxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; PCI > > <linux-pci@xxxxxxxxxxxxxxx>; Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; > > Gustavo Pimentel <gustavo.pimentel@xxxxxxxxxxxx>; Michael Walle > > <michael@xxxxxxxx>; Ard Biesheuvel <ardb@xxxxxxxxxx> > > Subject: Re: [PATCH] PCI: dwc: Added link up check in map_bus of > > dw_child_pcie_ops > > > > On Thu, Sep 24, 2020 at 04:24:47AM +0000, Z.q. Hou wrote: > > > Hi Rob, > > > > > > Thanks a lot for your comments! > > > > > > > -----Original Message----- > > > > From: Rob Herring <robh@xxxxxxxxxx> > > > > Sent: 2020年9月18日 23:28 > > > > To: Z.q. Hou <zhiqiang.hou@xxxxxxx> > > > > Cc: linux-kernel@xxxxxxxxxxxxxxx; PCI <linux-pci@xxxxxxxxxxxxxxx>; > > > > Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>; Bjorn Helgaas > > > > <bhelgaas@xxxxxxxxxx>; Gustavo Pimentel > > > > <gustavo.pimentel@xxxxxxxxxxxx>; Michael Walle > > <michael@xxxxxxxx>; > > > > Ard Biesheuvel <ardb@xxxxxxxxxx> > > > > Subject: Re: [PATCH] PCI: dwc: Added link up check in map_bus of > > > > dw_child_pcie_ops > > > > > > > > On Fri, Sep 18, 2020 at 5:02 AM Z.q. Hou <zhiqiang.hou@xxxxxxx> > > wrote: > > > > > > > > > > Hi Rob, > > > > > > > > > > Thanks a lot for your comments! > > > > > > > > > > > -----Original Message----- > > > > > > From: Rob Herring <robh@xxxxxxxxxx> > > > > > > Sent: 2020年9月17日 4:29 > > > > > > To: Z.q. Hou <zhiqiang.hou@xxxxxxx> > > > > > > Cc: linux-kernel@xxxxxxxxxxxxxxx; PCI > > > > > > <linux-pci@xxxxxxxxxxxxxxx>; Lorenzo Pieralisi > > > > > > <lorenzo.pieralisi@xxxxxxx>; Bjorn Helgaas > > > > > > <bhelgaas@xxxxxxxxxx>; Gustavo Pimentel > > > > > > <gustavo.pimentel@xxxxxxxxxxxx>; Michael Walle > > > > <michael@xxxxxxxx>; > > > > > > Ard Biesheuvel <ardb@xxxxxxxxxx> > > > > > > Subject: Re: [PATCH] PCI: dwc: Added link up check in map_bus of > > > > > > dw_child_pcie_ops > > > > > > > > > > > > On Tue, Sep 15, 2020 at 11:49 PM Zhiqiang Hou > > > > <Zhiqiang.Hou@xxxxxxx> > > > > > > wrote: > > > > > > > > > > > > > > From: Hou Zhiqiang <Zhiqiang.Hou@xxxxxxx> > > > > > > > > > > > > > > On NXP Layerscape platforms, it results in SError in the > > > > > > > enumeration of the PCIe controller, which is not connecting > > > > > > > with an Endpoint device. And it doesn't make sense to > > > > > > > enumerate the Endpoints when the PCIe link is down. So this > > > > > > > patch added the link up check to avoid to fire configuration > > transactions on link down bus. > > > > > > > > > > > > Michael reported the same issue as well. > > > > > > > > > > > > What happens if the link goes down between the check and the > > access? > > > > > > > > > > This patch cannot cover this case, and will get the SError. > > > > > But I think it makes sense to avoid firing transactions on link down bus. > > > > > > > > That's impossible to do without a race even in h/w. > > > > > > Agree. > > > > > > > > > > > > > It's a racy check. I'd like to find an alternative solution. > > > > > > It's even worse if Layerscape is used in ECAM mode. I looked at > > > > > > the EDK2 setup for layerscape[1] and it looks like root ports > > > > > > are just skipped if link > > > > is down. > > > > > > Maybe a link down just never happens once up, but if so, then we > > > > > > only need to check it once and fail probe. > > > > > > > > > > Many customers connect the FPGA Endpoint, which may establish PCIe > > > > > link after the PCIe enumeration and then rescan the PCIe bus, so I > > > > > think it should not exit the probe of root port even if there is > > > > > not link up > > > > during enumeration. > > > > > > > > That's a good reason. I want to unify the behavior here as it varies > > > > per platform currently and wasn't sure which way to go. > > > > > > > > > > > > > > I've dug into this a bit more and am curious about the > > > > > > PCIE_ABSERR register setting which is set to: > > > > > > > > > > > > #define PCIE_ABSERR_SETTING 0x9401 /* Forward error of > > > > > > non-posted request */ > > > > > > > > > > > > It seems to me this is not what we want at least for config > > > > > > accesses, but commit 84d897d6993 where this was added seems to > > > > > > say otherwise. Is it not possible to configure the response per access > > type? > > > > > > > > > > Thanks a lot for your investigation! > > > > > The story is like this: Some customers worry about these silent > > > > > error (DWC PCIe IP won't forward the error of outbound non-post > > > > > request by default), so we were pushed to enable the error > > > > > forwarding to AXI in the commit > > > > > 84d897d6993 as you saw. But it cannot differentiate the config > > > > > transactions from the MEM_rd, except the Vendor ID access, which > > > > > is controlled by a separate bit and it was set to not forward > > > > > error of access > > > > of Vendor ID. > > > > > So we think it's okay to enable the error forwarding, the SError > > > > > should not occur, because after the enumeration it won't access > > > > > the > > > > non-existent functions. > > > > > > > > We've rejected upstream support for platforms aborting on config > > > > accesses[1]. I think there's clear consensus that aborting is the > > > > wrong behavior. > > > > > > > > Do MEM_wr errors get forwarded? Seems like that would be enough. > > > > Also, wouldn't page faults catch most OOB accesses anyways? You need > > > > things page aligned anyways with an IOMMU and doing userspace access > > > > or guest assignment. > > > > > > Yes, errors of MEM_wr can be forwarded. > > > > > > > > > > > Here's another idea, how about only enabling forwarding errors if > > > > the link is up? If really would need to be configured any time the > > > > link state changes rather than just at probe. I'm not sure if you > > > > have a way to disable it on link down though. > > > > > > Dug deeper into this issue and found the setting of not forwarding > > > error of non-existent Vender ID access counts on the link partner: 1. > > > When there is a link partner (namely link up), it will return 0xffff > > > when read non-existent function Vendor ID and won't forward error to > > > AXI. 2. When no link partner (link down), it will forward the error > > > of reading non-existent function Vendor ID to AXI and result in > > > SError. > > > > > > I think this is a DWC PCIe IP specific issue but not get feedback from > > > design team. I'm thinking to disable this error forwarding just like > > > other platforms, since when these errors (UR, CA and CT) are detected, > > > AER driver can also report the error and try to recover. > > > > I take this as you shall send a patch to fix this issue shortly, is this correct ? > > The issue becomes complex: > I reviewed the DWC PCIe databook of verion 4.40a which is used on Layerscape platforms, and it said that " Your RC application should not generate CFG requests until it has confirmed that the link is up by sampling the smlh_link_up and rmlh_link_up outputs". > So, the link up checking should not be remove before each outbound CFG access. > Gustavo, can you share more details on the link up checking? Does it only exist in the 4.40a? Hi Zhiqiang, According to the information that I got from the IP team you are correct, the same requirement still exists on the newer IP versions. -Gustavo > > For the feature of error forwarding to AXI that enabled on Layerscape PCIe, I will send a patch to disable it today. > > Thanks, > Zhiqiang > > > > > Thanks, > > Lorenzo
