On Wed, Sep 30, 2020 at 8:22 AM Kishon Vijay Abraham I <kis...@ti.com> wrote: > > Hi, > > On 29/09/20 10:41 pm, Rob Herring wrote: > > On Tue, Sep 29, 2020 at 10:24 AM Gustavo Pimentel > > <gustavo.pimen...@synopsys.com> wrote: > >> > >> On Tue, Sep 29, 2020 at 5:5:41, Z.q. Hou <zhiqiang....@nxp.com> wrote: > >> > >>> Hi Lorenzo, > >>> > >>> Thanks a lot for your comments! > >>> > >>>> -----Original Message----- > >>>> From: Lorenzo Pieralisi <lorenzo.pieral...@arm.com> > >>>> Sent: 2020年9月28日 17:39 > >>>> To: Z.q. Hou <zhiqiang....@nxp.com> > >>>> Cc: Rob Herring <r...@kernel.org>; linux-kernel@vger.kernel.org; PCI > >>>> <linux-...@vger.kernel.org>; Bjorn Helgaas <bhelg...@google.com>; > >>>> Gustavo Pimentel <gustavo.pimen...@synopsys.com>; Michael Walle > >>>> <mich...@walle.cc>; Ard Biesheuvel <a...@kernel.org> > >>>> 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 <r...@kernel.org> > >>>>>> Sent: 2020年9月18日 23:28 > >>>>>> To: Z.q. Hou <zhiqiang....@nxp.com> > >>>>>> Cc: linux-kernel@vger.kernel.org; PCI <linux-...@vger.kernel.org>; > >>>>>> Lorenzo Pieralisi <lorenzo.pieral...@arm.com>; Bjorn Helgaas > >>>>>> <bhelg...@google.com>; Gustavo Pimentel > >>>>>> <gustavo.pimen...@synopsys.com>; Michael Walle > >>>> <mich...@walle.cc>; > >>>>>> Ard Biesheuvel <a...@kernel.org> > >>>>>> 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....@nxp.com> > >>>> wrote: > >>>>>>> > >>>>>>> Hi Rob, > >>>>>>> > >>>>>>> Thanks a lot for your comments! > >>>>>>> > >>>>>>>> -----Original Message----- > >>>>>>>> From: Rob Herring <r...@kernel.org> > >>>>>>>> Sent: 2020年9月17日 4:29 > >>>>>>>> To: Z.q. Hou <zhiqiang....@nxp.com> > >>>>>>>> Cc: linux-kernel@vger.kernel.org; PCI > >>>>>>>> <linux-...@vger.kernel.org>; Lorenzo Pieralisi > >>>>>>>> <lorenzo.pieral...@arm.com>; Bjorn Helgaas > >>>>>>>> <bhelg...@google.com>; Gustavo Pimentel > >>>>>>>> <gustavo.pimen...@synopsys.com>; Michael Walle > >>>>>> <mich...@walle.cc>; > >>>>>>>> Ard Biesheuvel <a...@kernel.org> > >>>>>>>> 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....@nxp.com> > >>>>>>>> wrote: > >>>>>>>>> > >>>>>>>>> From: Hou Zhiqiang <zhiqiang....@nxp.com> > >>>>>>>>> > >>>>>>>>> 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. > > > > How is that possible in a race free way? > > > > Testing on meson and layerscape (with the forwarding of errors > > disabled) shows a link check is not needed. But then dra7xx seems to > > need one (or has some f/w setup). > > Yeah, I don't see any registers in the DRA7x PCIe wrapper for disabling > error forwarding.
It's a DWC port logic register AFAICT, but perhaps not present in all versions. Rob
