linux-kernel - Re: Help needed in understanding weird PCIe issue on imx6q (PCIe just goes bad)

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Message-ID: <CAGgoGu6xQ2aV5kcmxcOm2Q=zPEY3mu3fOaCXKPxaz17vptzcmA@mail.gmail.com>
Date:   Tue, 25 Feb 2020 10:00:14 +0100
From:   Fawad Lateef <fawadlateef@...il.com>
To:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org
Subject: Re: Help needed in understanding weird PCIe issue on imx6q (PCIe just
 goes bad)

Hi again,

Can someone guide me what is going on?

Thanks,

-- Fawad Lateef

On Sat, 22 Feb 2020 at 16:25, Fawad Lateef <fawadlateef@...il.com> wrote:
>
> Hello,
>
> I am trying to figure-out an issue on our i.MX6Q platform based design
> where PCIe interface goes bad.
>
> We have a Phytec i.MX6Q eMMC SOM, attached to our custom designed
> board. PCIe root-complex from i.MX6Q is attached to PLX switch
> (PEX8605).
>
> Linux kernel version is 4.19.9x and also 4.14.134 (from phytec's
> linux-mainline repo). Kernel do not have PCIe hot-plug and PNP enabled
> in config.
>
> PLX switch #PERST is attached to a GPIO pin and stays in disable state
> until Linux is booted. So at boot time only PCIe root-complex is
> initialized by kernel.
>
> After boot if I do "lspci -v"  and see everything good from PCIe
> root-complex (below):
>
> ~ # lspci -v
> 00:00.0 PCI bridge: Synopsys, Inc. Device abcd (rev 01) (prog-if 00
> [Normal decode])
> Flags: bus master, fast devsel, latency 0, IRQ 295
> Memory at 01000000 (32-bit, non-prefetchable) [size=1M]
> Bus: primary=00, secondary=01, subordinate=ff, sec-latency=0
> I/O behind bridge: None
> Memory behind bridge: None
> Prefetchable memory behind bridge: None
> [virtual] Expansion ROM at 01100000 [disabled] [size=64K]
> Capabilities: [40] Power Management version 3
> Capabilities: [50] MSI: Enable+ Count=1/1 Maskable+ 64bit+
> Capabilities: [70] Express Root Port (Slot-), MSI 00
> Capabilities: [100] Advanced Error Reporting
> Capabilities: [140] Virtual Channel
> Kernel driver in use: pcieport
>
>
> Then I enable the #PERST pin of PLX switch, everything is still good
> (no rescan on Linux is done yet)
>
> ~ # echo 139 > /sys/class/gpio/export
> ~ # echo out > /sys/class/gpio/gpio139/direction
> ~ # echo 1 > /sys/class/gpio/gpio139/value
> ~ # lspci -v
> 00:00.0 PCI bridge: Synopsys, Inc. Device abcd (rev 01) (prog-if 00
> [Normal decode])
> Flags: bus master, fast devsel, latency 0, IRQ 295
> Memory at 01000000 (32-bit, non-prefetchable) [size=1M]
> Bus: primary=00, secondary=01, subordinate=ff, sec-latency=0
> I/O behind bridge: None
> Memory behind bridge: None
> Prefetchable memory behind bridge: None
> [virtual] Expansion ROM at 01100000 [disabled] [size=64K]
> Capabilities: [40] Power Management version 3
> Capabilities: [50] MSI: Enable+ Count=1/1 Maskable+ 64bit+
> Capabilities: [70] Express Root Port (Slot-), MSI 00
> Capabilities: [100] Advanced Error Reporting
> Capabilities: [140] Virtual Channel
> Kernel driver in use: pcieport
>
>
> Now just disable/put-in-reset the PLX switch (Linux don't see the
> switch yet, as no rescan on PCIe was done). Now "lspci -v" and
> root-complex goes bad.
>
> ~ # echo 0 > /sys/class/gpio/gpio139/value
> ~ # lspci -v
> 00:00.0 PCI bridge: Synopsys, Inc. Device abcd (rev 01) (prog-if 00
> [Normal decode])
> Flags: fast devsel, IRQ 295
> Memory at 01000000 (64-bit, prefetchable) [disabled] [size=1M]
> Bus: primary=00, secondary=00, subordinate=00, sec-latency=0
> I/O behind bridge: 00000000-00000fff [size=4K]
> Memory behind bridge: 00000000-000fffff [size=1M]
> Prefetchable memory behind bridge: 00000000-000fffff [size=1M]
> [virtual] Expansion ROM at 01100000 [disabled] [size=64K]
> Capabilities: [40] Power Management version 3
> Capabilities: [50] MSI: Enable- Count=1/1 Maskable+ 64bit+
> Capabilities: [70] Express Root Port (Slot-), MSI 00
> Capabilities: [100] Advanced Error Reporting
> Capabilities: [140] Virtual Channel
> Kernel driver in use: pcieport
>
> ~ # uname -a
> Linux buildroot-2019.08-imx6 4.14.134-phy2 #1 SMP Thu Feb 20 12:13:33
> UTC 2020 armv7l GNU/Linux
> ~ #
>
>
> I am really not sure what is going wrong here. Did I am missing
> something basic?
>
> Thanks in advance,
>
> -- Fawad Lateef