linux-kernel - Re: Assistance Needed: PCIe Device BAR Reset Issue

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Message-ID: <Z5y9j0eOQTIrcD7E@wunner.de>
Date: Fri, 31 Jan 2025 13:09:51 +0100
From: Lukas Wunner <lukas@...ner.de>
To: Naveen Kumar P <naveenkumar.parna@...il.com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bjorn Helgaas <helgaas@...nel.org>
Subject: Re: Assistance Needed: PCIe Device BAR Reset Issue

On Fri, Jan 31, 2025 at 03:37:26PM +0530, Naveen Kumar P wrote:
> PCIe Device: PLDA Device 5555
[...]
> Initially, the BAR value is 0xb0400000. However, after some time, reading
> from the PCIe device's BAR memory fails and returns 0xffff

If you're reading "all ones" from config space, it means the device is
inaccessible and the host bridge is returning this fabricated value after
a timeout.

>         Kernel modules: m1801_pci

That's not a driver in the upstream kernel.

Maybe that driver allows the device to runtime suspend to D3hot,
which in turn allows its upstream bridge to also runtime suspend
to D3hot.  Then the device would be inaccessible.

> Verified power management settings:
> 
> cat /sys/module/pcie_aspm/parameters/policy
> Output: [default] performance powersave powersupersave

/sys/bus/pci/devices/0000:01:00.0/power/runtime_status
would tell you whether the device is runtime suspended.

Thanks,

Lukas