Messages in this thread | | | Date | Wed, 25 May 2022 09:21:24 +0200 | Subject | Re: [PATCH v1] PCI: brcmstb: Fix regression regarding missing PCIe linkup | From | Stefan Wahren <> |
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Hi Jim,
Am 24.05.22 um 18:54 schrieb Jim Quinlan: > On Mon, May 23, 2022 at 6:10 PM Bjorn Helgaas <helgaas@kernel.org> wrote: >> On Sat, May 21, 2022 at 02:51:42PM -0400, Jim Quinlan wrote: >>> On Sat, May 21, >>> 2CONFIG_INITRAMFS_SOURCE="/work3/jq921458/cpio/54-arm64-rootfs.cpio022 >>> at 12:43 PM Bjorn Helgaas <helgaas@kernel.org> wrote: >>>> On Wed, May 18, 2022 at 03:42:11PM -0400, Jim Quinlan wrote: >>>>> commit 93e41f3fca3d ("PCI: brcmstb: Add control of subdevice >>>>> voltage regulators") >>>>> >>>>> introduced a regression on the PCIe RPi4 Compute Module. If the >>>>> PCIe endpoint node described in [2] was missing, no linkup would >>>>> be attempted, and subsequent accesses would cause a panic >>>>> because this particular PCIe HW causes a CPU abort on illegal >>>>> accesses (instead of returning 0xffffffff). >>>>> >>>>> We fix this by allowing the DT endpoint subnode to be missing. >>>>> This is important for platforms like the CM4 which have a >>>>> standard PCIe socket and the endpoint device is unknown. >>>> I think the problem here is that on the CM, we try to enumerate >>>> devices that are not powered up, isn't it? The commit log should >>>> say something about that power situation and how the driver learns >>>> about the power regulators instead of just pointing at an DT >>>> endpoint node. >>> This is incorrect. The regression occurred because the code >>> mistakenly skips PCIe-linkup if the PCI portdrv DT node does not >>> exist. With our RC HW, doing a config space access to bus 1 w/o >>> first linking up results in a CPU abort. This regression has >>> nothing to do with EP power at all. >> OK, I think I'm starting to see, but I'm still missing some things. >> >> 67211aadcb4b ("PCI: brcmstb: Add mechanism to turn on subdev >> regulators") added pci_subdev_regulators_add_bus() as an .add_bus() >> method. This is called by pci_alloc_child_bus(), and if the DT >> describes any regulators for the bridge leading to the new child bus, >> we turn them on. >> >> Then 93e41f3fca3d ("PCI: brcmstb: Add control of subdevice voltage >> regulators") added brcm_pcie_add_bus() and made *it* the .add_bus() >> method. It turns on the regulators and brings the link up, but it >> skips both if there's no DT node for the bridge to the new bus. > Hi Bjorn, > > Yes, I meant it to skip the turning on of the regulators if the DT > node was missing > but I failed to notice that it would also skip the pcie linkup as well. As you > may have guessed, all of my test systems have the PCIe root port > DT node. > >> I guess RPi4 CM has no DT node to describe regulators, so we skip both >> turning them on *and* bringing the link up? > Yes. One repo did not have this node (Cyril/debina?), one did > (https://github.com/raspberrypi/firmware/tree/master/boot). > Of course there is nothing wrong with omitting the node; it should > have pcie linkup regardless. Please ignore the vendor tree, because you only have to care about mainline kernel and DT here. > >> But above you say it's the *endpoint* node that doesn't exist. The >> existing code looks like it's checking for the *bridge* node >> (bus->dev->of_node). We haven't even enumerated the devices on the >> child bus, so we don't know about them at this point. > You are absolutely correct and I must change the commit message > to say the "root port DT node". I'm sorry; this mistake likely did not > help you understand the fix. :-( > >> What happens if there is a DT node for the bridge, but it doesn't >> describe any regulators? I assume regulator_bulk_get() will fail, and >> it looks like that might still keep us from bringing the link up? > The regulator_bulk_get() func does not fail if the regulators are not > present. Instead it "gets" > a dummy device and issues a warning per missing regulator. > A version of my pullreq submitted code to prescan the DT node and call > regulator_bulk_get() with > only the names of the regulators present, but IIRC this was NAKd. > Hopefully I will not be swamped with RPi developers' emails when they > think these warnings are an issue.
This won't be the first driver complaining about missing regulators and won't be the last one. So don't expect an email from me ;-)
Best regards
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