Re: [PATCH v7] PCI/PM: Skip resuming to D0 if device is disconnected

[Mario Limonciello <superm1@kernel.org>]

On 9/18/25 5:08 PM, Bjorn Helgaas wrote:
> On Mon, Sep 08, 2025 at 10:19:15PM -0500, Mario Limonciello (AMD) wrote:
>> From: Mario Limonciello <mario.limonciello@amd.com>
>>
>> When a PCIe device is surprise-removed (e.g., due to a dock unplug),
>> the PCI core unconfigures all downstream devices and sets their error
>> state to `pci_channel_io_perm_failure`. This marks them as disconnected
>> via `pci_dev_is_disconnected()`.
>>
>> During device removal, the runtime PM framework may attempt to resume
>> the device to D0 via `pm_runtime_get_sync()`, which calls into
>> `pci_power_up()`. Since the device is already disconnected, this
>> resume attempt is unnecessary and results in a predictable error.
>> Avoid powering up disconnected devices by checking their status early
>> in `pci_power_up()` and returning -EIO.
> 
> Hi Mario,
> 
> I forgot to ask if there are any characteristic dmesg logs and user
> activities that we could include here to help users recognize this
> problem.  I suppose it results in messages like this?
> 
>    pci 0000:01:00.0: Unable to change power state from D3cold to D0, device inaccessible
> 
> Maybe especially when undocking?  Although oddly a google search for
> that message and "undock" finds nothing.
> 

Yes spot on.  The dock needs to be TBT3 or USB4 and the host has to 
offer PCIe tunneling for it to occur.

>> Suggested-by: Lukas Wunner <lukas@wunner.de>
>> Reviewed-by: Lukas Wunner <lukas@wunner.de>
>> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
>> Acked-by: Rafael J. Wysocki <rafael@kernel.org>
>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>> ---
>> v7:
>>   * Reword commit message
>>   * Rebase on v6.17-rc5
>> ---
>>   drivers/pci/pci.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index b0f4d98036cdd..036511f5b2625 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -1374,6 +1374,11 @@ int pci_power_up(struct pci_dev *dev)
>>   		return -EIO;
>>   	}
>>   
>> +	if (pci_dev_is_disconnected(dev)) {
>> +		dev->current_state = PCI_D3cold;
>> +		return -EIO;
>> +	}
>> +
>>   	pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
>>   	if (PCI_POSSIBLE_ERROR(pmcsr)) {
>>   		pci_err(dev, "Unable to change power state from %s to D0, device inaccessible\n",
>> -- 
>> 2.43.0
>>