linux-kernel - Re: [PATCH] PCI: keystone: Don't enable BAR0 if link is not detected

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Message-ID: <5613f8e1-9c73-18c3-8a19-9a164b09b577@ti.com>
Date:   Fri, 13 Oct 2023 10:33:06 +0530
From:   Siddharth Vadapalli <s-vadapalli@...com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     <lpieralisi@...nel.org>, <robh@...nel.org>, <kw@...ux.com>,
        <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <r-gunasekaran@...com>,
        <srk@...com>, <s-vadapalli@...com>
Subject: Re: [PATCH] PCI: keystone: Don't enable BAR0 if link is not detected



On 12/10/23 22:13, Bjorn Helgaas wrote:
> On Thu, Oct 12, 2023 at 10:15:09AM +0530, Siddharth Vadapalli wrote:
>> Hello Bjorn,
>>
>> Thank you for reviewing the patch.
>>
>> On 11/10/23 19:16, Bjorn Helgaas wrote:
>>> Hi Siddharth,
>>>

...

>>                                               msix_prepare_msi_desc
>> In this function: msix_prepare_msi_desc, the following readl()
>> causes completion timeout:
>> 		desc->pci.msix_ctrl = readl(addr + PCI_MSIX_ENTRY_VECTOR_CTRL);
>> The completion timeout with the readl is only observed when the link
>> is down (No Endpoint device is actually connected to the PCIe
>> connector slot).
> 
> Do you know the address ("addr")?  From pci_msix_desc_addr(), it looks
> like it should be:
> 
>   desc->pci.mask_base + desc->msi_index * PCI_MSIX_ENTRY_SIZE
> 
> and desc->pci.mask_base should be dev->msix_base, which we got from
> msix_map_region(), which ioremaps part of the BAR indicated by the
> MSI-X Table Offset/Table BIR register.
> 
> I wonder if this readl() is being handled as an MMIO access to a
> downstream device instead of a Root Port BAR access because it's
> inside the Root Port's MMIO window.
> 
> Could you dump out these values just before the readl()?
> 
>   phys_addr inside msix_map_region()
>   dev->msix_base
>   desc->pci.mask_base
>   desc->msi_index
>   addr

phys_addr: 0x10102000
msix_base: 0xffff80000997a000
mask_base: 0xffff80000997a000
msi_index: 0
addr: 0xffff80000997a000

Also, the details of BAR allocation from the logs are:
keystone-pcie 5500000.pcie: host bridge /bus@...000/pcie@...0000 ranges:
keystone-pcie 5500000.pcie:       IO 0x0010020000..0x001002ffff -> 0x0000000000
keystone-pcie 5500000.pcie:      MEM 0x0010030000..0x0017ffffff -> 0x0010030000
keystone-pcie 5500000.pcie: iATU unroll: enabled
keystone-pcie 5500000.pcie: iATU regions: 8 ob, 8 ib, align 64K, limit 4G
keystone-pcie 5500000.pcie: Phy link never came up
keystone-pcie 5500000.pcie: PCI host bridge to bus 0000:00
pci_bus 0000:00: root bus resource [bus 00-ff]
pci_bus 0000:00: root bus resource [io  0x0000-0xffff]
pci_bus 0000:00: root bus resource [mem 0x10030000-0x17ffffff]
pci 0000:00:00.0: [104c:b00c] type 01 class 0x060400
pci 0000:00:00.0: reg 0x10: [mem 0x05500000-0x055fffff]
pci 0000:00:00.0: reg 0x38: [mem 0x00000000-0x0000ffff pref]
pci 0000:00:00.0: supports D1
pci 0000:00:00.0: PME# supported from D0 D1 D3hot
pci 0000:00:00.0: BAR 0: assigned [mem 0x10100000-0x101fffff]
pci 0000:00:00.0: BAR 6: assigned [mem 0x10030000-0x1003ffff pref]
pci 0000:00:00.0: PCI bridge to [bus 01-ff]

The value of phys_addr lies within the range allocated to BAR0.

>   call early_dump_pci_device() on the Root Port

I invoked early_dump_pci_device() within the pci_setup_device() function in
drivers/pci/probe.c and the output is:

pci 0000:00:00.0: config space:
00000000: 4c 10 0c b0 07 01 10 00 01 00 04 06 00 00 01 00
00000010: 00 00 50 05 00 00 00 00 00 01 ff 00 00 00 00 00
00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00000030: 00 00 00 00 40 00 00 00 00 00 00 00 ff 01 00 00
00000040: 01 50 c3 5b 08 00 00 00 00 00 00 00 00 00 00 00
00000050: 05 70 80 01 00 00 00 00 00 00 00 00 00 00 00 00
00000060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00000070: 10 b0 42 00 01 80 00 00 10 20 00 00 22 3c 73 00
00000080: 00 00 11 10 00 00 00 00 c0 03 40 00 00 00 01 00
00000090: 00 00 00 00 1f 04 00 00 00 00 00 00 06 00 00 00
000000a0: 02 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00
000000b0: 11 00 00 01 00 20 00 00 00 40 00 00 00 00 00 00
000000c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
000000d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
000000e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
000000f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00


> 
> Bjorn

-- 
Regards,
Siddharth.