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SubjectRe: [PATCH] PCI: dwc: Added link up check in map_bus of dw_child_pcie_ops
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Hi Hou,

On 19/10/20 10:54 am, Z.q. Hou wrote:
> Hello Bjorn,
>
> Thanks a lot for your comments!
>
>> -----Original Message-----
>> From: Bjorn Helgaas <helgaas@kernel.org>
>> Sent: 2020年10月16日 6:48
>> To: Z.q. Hou <zhiqiang.hou@nxp.com>
>> Cc: linux-kernel@vger.kernel.org; linux-pci@vger.kernel.org;
>> robh@kernel.org; lorenzo.pieralisi@arm.com; bhelgaas@google.com;
>> gustavo.pimentel@synopsys.com
>> Subject: Re: [PATCH] PCI: dwc: Added link up check in map_bus of
>> dw_child_pcie_ops
>>
>> On Wed, Sep 16, 2020 at 01:41:30PM +0800, Zhiqiang Hou wrote:
>>> From: Hou Zhiqiang <Zhiqiang.Hou@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.
>>
>> Lorenzo already applied this, but a couple questions:
>>
>> You call out NXP Layerscape specifically, but doesn't this affect other
>> DWC-based platforms, too? You later mentioned imx6, Kishon mentioned
>> dra7xx, Michael mentioned ls1028a, Naresh mentioned ls2088 (probably
>> both the same as your "NXP Layerscape").
>
> For NXP Layerscape platforms (the ls1028a and ls2088a are also NXP Layerscape platform), as the error response to AXI/AHB was enabled, it will get UR error and trigger SError on AXI bus when it accesses a non-existent BDF on a link down bus. I'm not clear about how it happens on dra7xxx and imx6, since they doesn't enable the error response to AXI/AHB.

That's exactly the case with DRA7xx as the error response is enabled by
default in the platform integration.

Thanks
Kishon

>
>>
>> The backtrace below contains a bunch of irrelevant info. The timestamps
>> are pointless. The backtrace past
>> pci_scan_single_device+0x80/0x100 or so really doesn't add anything either.
>>
>> It'd be nice to have a comment in the code because the code *looks* wrong
>> and racy. Without a hint, everybody who sees it will have to dig through
>> the history to see why we tolerate the race.
>
> Yes, agree, but seems the cause of the SError on dra7xx and imx6 is different from Layerscape platforms, we need to make it clear first.
>
> Thanks,
> Zhiqiang
>
>>
>>> [ 0.807773] SError Interrupt on CPU2, code 0xbf000002 -- SError
>>> [ 0.807775] CPU: 2 PID: 1 Comm: swapper/0 Not tainted
>> 5.9.0-rc5-next-20200914-00001-gf965d3ec86fa #67
>>> [ 0.807776] Hardware name: LS1046A RDB Board (DT)
>>> [ 0.807777] pstate: 20000085 (nzCv daIf -PAN -UAO BTYPE=--)
>>> [ 0.807778] pc : pci_generic_config_read+0x3c/0xe0
>>> [ 0.807778] lr : pci_generic_config_read+0x24/0xe0
>>> [ 0.807779] sp : ffff80001003b7b0
>>> [ 0.807780] x29: ffff80001003b7b0 x28: ffff80001003ba74
>>> [ 0.807782] x27: ffff000971d96800 x26: ffff00096e77e0a8
>>> [ 0.807784] x25: ffff80001003b874 x24: ffff80001003b924
>>> [ 0.807786] x23: 0000000000000004 x22: 0000000000000000
>>> [ 0.807788] x21: 0000000000000000 x20: ffff80001003b874
>>> [ 0.807790] x19: 0000000000000004 x18: ffffffffffffffff
>>> [ 0.807791] x17: 00000000000000c0 x16: fffffe0025981840
>>> [ 0.807793] x15: ffffb94c75b69948 x14: 62203a383634203a
>>> [ 0.807795] x13: 666e6f635f726568 x12: 202c31203d207265
>>> [ 0.807797] x11: 626d756e3e2d7375 x10: 656877202c307830
>>> [ 0.807799] x9 : 203d206e66766564 x8 : 0000000000000908
>>> [ 0.807801] x7 : 0000000000000908 x6 : ffff800010900000
>>> [ 0.807802] x5 : ffff00096e77e080 x4 : 0000000000000000
>>> [ 0.807804] x3 : 0000000000000003 x2 : 84fa3440ff7e7000
>>> [ 0.807806] x1 : 0000000000000000 x0 : ffff800010034000
>>> [ 0.807808] Kernel panic - not syncing: Asynchronous SError Interrupt
>>> [ 0.807809] CPU: 2 PID: 1 Comm: swapper/0 Not tainted
>> 5.9.0-rc5-next-20200914-00001-gf965d3ec86fa #67
>>> [ 0.807810] Hardware name: LS1046A RDB Board (DT)
>>> [ 0.807811] Call trace:
>>> [ 0.807812] dump_backtrace+0x0/0x1c0
>>> [ 0.807813] show_stack+0x18/0x28
>>> [ 0.807814] dump_stack+0xd8/0x134
>>> [ 0.807814] panic+0x180/0x398
>>> [ 0.807815] add_taint+0x0/0xb0
>>> [ 0.807816] arm64_serror_panic+0x78/0x88
>>> [ 0.807817] do_serror+0x68/0x180
>>> [ 0.807818] el1_error+0x84/0x100
>>> [ 0.807818] pci_generic_config_read+0x3c/0xe0
>>> [ 0.807819] dw_pcie_rd_other_conf+0x78/0x110
>>> [ 0.807820] pci_bus_read_config_dword+0x88/0xe8
>>> [ 0.807821] pci_bus_generic_read_dev_vendor_id+0x30/0x1b0
>>> [ 0.807822] pci_bus_read_dev_vendor_id+0x4c/0x78
>>> [ 0.807823] pci_scan_single_device+0x80/0x100
>>> [ 0.807824] pci_scan_slot+0x38/0x130
>>> [ 0.807825] pci_scan_child_bus_extend+0x54/0x2a0
>>> [ 0.807826] pci_scan_child_bus+0x14/0x20
>>> [ 0.807827] pci_scan_bridge_extend+0x230/0x570
>>> [ 0.807828] pci_scan_child_bus_extend+0x134/0x2a0
>>> [ 0.807829] pci_scan_root_bus_bridge+0x64/0xf0
>>> [ 0.807829] pci_host_probe+0x18/0xc8
>>> [ 0.807830] dw_pcie_host_init+0x220/0x378
>>> [ 0.807831] ls_pcie_probe+0x104/0x140
>>> [ 0.807832] platform_drv_probe+0x54/0xa8
>>> [ 0.807833] really_probe+0x118/0x3e0
>>> [ 0.807834] driver_probe_device+0x5c/0xc0
>>> [ 0.807835] device_driver_attach+0x74/0x80
>>> [ 0.807835] __driver_attach+0x8c/0xd8
>>> [ 0.807836] bus_for_each_dev+0x7c/0xd8
>>> [ 0.807837] driver_attach+0x24/0x30
>>> [ 0.807838] bus_add_driver+0x154/0x200
>>> [ 0.807839] driver_register+0x64/0x120
>>> [ 0.807839] __platform_driver_probe+0x7c/0x148
>>> [ 0.807840] ls_pcie_driver_init+0x24/0x30
>>> [ 0.807841] do_one_initcall+0x60/0x1d8
>>> [ 0.807842] kernel_init_freeable+0x1f4/0x24c
>>> [ 0.807843] kernel_init+0x14/0x118
>>> [ 0.807843] ret_from_fork+0x10/0x34
>>> [ 0.807854] SMP: stopping secondary CPUs
>>> [ 0.807855] Kernel Offset: 0x394c64080000 from 0xffff800010000000
>>> [ 0.807856] PHYS_OFFSET: 0xffff8bfd40000000
>>> [ 0.807856] CPU features: 0x0240022,21806000
>>> [ 0.807857] Memory Limit: none
>>>
>>> Fixes: c2b0c098fbd1 ("PCI: dwc: Use generic config accessors")
>>> Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
>>> ---
>>> drivers/pci/controller/dwc/pcie-designware-host.c | 6 ++++++
>>> 1 file changed, 6 insertions(+)
>>>
>>> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c
>>> b/drivers/pci/controller/dwc/pcie-designware-host.c
>>> index c01c9d2fb3f9..e82b518430c5 100644
>>> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
>>> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
>>> @@ -442,6 +442,9 @@ static void __iomem
>> *dw_pcie_other_conf_map_bus(struct pci_bus *bus,
>>> struct pcie_port *pp = bus->sysdata;
>>> struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
>>>
>>> + if (!dw_pcie_link_up(pci))
>>> + return NULL;
>>> +
>>> busdev = PCIE_ATU_BUS(bus->number) |
>> PCIE_ATU_DEV(PCI_SLOT(devfn)) |
>>> PCIE_ATU_FUNC(PCI_FUNC(devfn));
>>>
>>> --
>>> 2.17.1
>>>

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