linux-kernel - Re: [PATCH v2 1/4] PCI: Check PCI_PM_CTRL in pci_dev

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Message-ID: <dcaefa84-09f5-4be5-9f66-aac6bf5fabf7@kernel.org>
Date: Thu, 11 Jul 2024 10:10:44 -0500
From: Mario Limonciello <superm1@...nel.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
 Mathias Nyman <mathias.nyman@...el.com>,
 Mika Westerberg <mika.westerberg@...ux.intel.com>,
 "open list : PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>,
 "open list : USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
 Daniel Drake <drake@...lessos.org>, Gary Li <Gary.Li@....com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v2 1/4] PCI: Check PCI_PM_CTRL in pci_dev_wait()

On 7/11/2024 10:07, Ilpo Järvinen wrote:
> On Wed, 10 Jul 2024, superm1@...nel.org wrote:
> 
>> From: Mario Limonciello <mario.limonciello@....com>
>>
>> A device that has gone through a reset may return a value in PCI_COMMAND
>> but that doesn't mean it's finished transitioning to D0.  On devices that
>> support power management explicitly check PCI_PM_CTRL on everything but
>> system resume to ensure the transition happened.
>>
>> Devices that don't support power management and system resume will
>> continue to use PCI_COMMAND.
>>
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>> ---
>>   drivers/pci/pci.c | 27 ++++++++++++++++++++-------
>>   1 file changed, 20 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index 35fb1f17a589c..4ad02ad640518 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -1270,21 +1270,34 @@ static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
>>   	 * the read (except when CRS SV is enabled and the read was for the
>>   	 * Vendor ID; in that case it synthesizes 0x0001 data).
>>   	 *
>> -	 * Wait for the device to return a non-CRS completion.  Read the
>> -	 * Command register instead of Vendor ID so we don't have to
>> -	 * contend with the CRS SV value.
>> +	 * Wait for the device to return a non-CRS completion.  On devices
>> +	 * that support PM control and on waits that aren't part of system
>> +	 * resume read the PM control register to ensure the device has
>> +	 * transitioned to D0.  On devices that don't support PM control,
>> +	 * or during system resume read the command register to instead of
>> +	 * Vendor ID so we don't have to contend with the CRS SV value.
>>   	 */
>>   	for (;;) {
>> -		u32 id;
>>   
>>   		if (pci_dev_is_disconnected(dev)) {
>>   			pci_dbg(dev, "disconnected; not waiting\n");
>>   			return -ENOTTY;
>>   		}
>>   
>> -		pci_read_config_dword(dev, PCI_COMMAND, &id);
>> -		if (!PCI_POSSIBLE_ERROR(id))
>> -			break;
>> +		if (dev->pm_cap && strcmp(reset_type, "resume") != 0) {
> 
> Comparing to a string makes me feel reset_type should be changed to
> something that allows direct compare and those values only mapped into
> string while printing it.
> 

Thanks, that's a great suggestion.  I'll add a patch earlier in the 
series to make an enum of the types instead and a mapping function for 
them to get the string as needed.