linux-kernel - Re: [PATCH] powerpc/pseries/msi: Avoid reading PCI device registers in reduced power states

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Message-ID: <87tt81tr8t.fsf@vajain21.in.ibm.com>
Date: Mon, 10 Mar 2025 10:30:02 +0530
From: Vaibhav Jain <vaibhav@...ux.ibm.com>
To: Gautam Menghani <gautam@...ux.ibm.com>, maddy@...ux.ibm.com,
        mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu,
        naveen@...nel.org
Cc: Gautam Menghani <gautam@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/pseries/msi: Avoid reading PCI device registers
 in reduced power states

Gautam Menghani <gautam@...ux.ibm.com> writes:

> When a system is being suspended to RAM, the PCI devices are also
> suspended and the PPC code ends up calling pseries_msi_compose_msg() and
> this triggers the BUG_ON() in __pci_read_msi_msg() because the device at
> this point is in reduced power state. In reduced power state, the memory
> mapped registers of the PCI device are not accessible.
>
> To replicate the bug:
> 1. Make sure deep sleep is selected
> 	# cat /sys/power/mem_sleep
> 	s2idle [deep]
>
> 2. Make sure console is not suspended (so that dmesg logs are visible)
> 	echo N > /sys/module/printk/parameters/console_suspend
>
> 3. Suspend the system
> 	echo mem > /sys/power/state
>
> To fix this behaviour, read the cached msi message of the device when the
> device is not in PCI_D0 power state instead of touching the hardware.
>
> Fixes: a5f3d2c17b07 ("powerpc/pseries/pci: Add MSI domains")
> Cc: stable@...r.kernel.org # v5.15+
> Signed-off-by: Gautam Menghani <gautam@...ux.ibm.com>
LGTM. Hence
Reviewed-by: Vaibhav Jain <vaibhav@...ux.ibm.com>

-- 
Cheers
~ Vaibhav