PCI/PM: Add comments for PME poll support for PCIe

Submitted by Huang Ying on Oct. 26, 2012, 5:07 a.m.

Details

Message ID 1351228071-15161-1-git-send-email-ying.huang@intel.com
State Accepted
Headers show

Commit Message

Huang Ying Oct. 26, 2012, 5:07 a.m.
There are comments on why PME poll support is necessary for PCI
devices, but not for PCIe devices.  That may lead to misunderstanding
that PME poll is only necessary for PCI devices.  So add comments
related to PCIe PME poll to make it more clear.

The content of comments comes from the changelog of commit:

379021d5c0899fcf9410cae4ca7a59a5a94ca769

Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Huang Ying <ying.huang@intel.com>
---
 drivers/pci/pci.c |   28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

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Comments

Rafael J. Wysocki Oct. 26, 2012, 11:18 a.m.
On Friday, October 26, 2012 01:07:51 PM Huang Ying wrote:
> There are comments on why PME poll support is necessary for PCI
> devices, but not for PCIe devices.  That may lead to misunderstanding
> that PME poll is only necessary for PCI devices.  So add comments
> related to PCIe PME poll to make it more clear.
> 
> The content of comments comes from the changelog of commit:
> 
> 379021d5c0899fcf9410cae4ca7a59a5a94ca769
> 
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Signed-off-by: Huang Ying <ying.huang@intel.com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
>  drivers/pci/pci.c |   28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1578,15 +1578,25 @@ void pci_pme_active(struct pci_dev *dev,
>  
>  	pci_write_config_word(dev, dev->pm_cap + PCI_PM_CTRL, pmcsr);
>  
> -	/* PCI (as opposed to PCIe) PME requires that the device have
> -	   its PME# line hooked up correctly. Not all hardware vendors
> -	   do this, so the PME never gets delivered and the device
> -	   remains asleep. The easiest way around this is to
> -	   periodically walk the list of suspended devices and check
> -	   whether any have their PME flag set. The assumption is that
> -	   we'll wake up often enough anyway that this won't be a huge
> -	   hit, and the power savings from the devices will still be a
> -	   win. */
> +	/*
> +	 * PCI (as opposed to PCIe) PME requires that the device have
> +	 * its PME# line hooked up correctly. Not all hardware vendors
> +	 * do this, so the PME never gets delivered and the device
> +	 * remains asleep. The easiest way around this is to
> +	 * periodically walk the list of suspended devices and check
> +	 * whether any have their PME flag set. The assumption is that
> +	 * we'll wake up often enough anyway that this won't be a huge
> +	 * hit, and the power savings from the devices will still be a
> +	 * win.
> +	 *
> +	 * Although PCIe uses in-band PME message instead of PME# line
> +	 * to report PME, PME does not work for some PCIe devices in
> +	 * reality.  For example, there are devices that set their PME
> +	 * status bits, but don't really bother to send a PME message;
> +	 * there are PCI Express Root Ports that don't bother to
> +	 * trigger interrupts when they receive PME messages from the
> +	 * devices below.  So PME poll is used for PCIe devices too.
> +	 */
>  
>  	if (dev->pme_poll) {
>  		struct pci_pme_device *pme_dev;
>
Bjorn Helgaas Nov. 5, 2012, 10:14 p.m.
On Fri, Oct 26, 2012 at 5:18 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> On Friday, October 26, 2012 01:07:51 PM Huang Ying wrote:
>> There are comments on why PME poll support is necessary for PCI
>> devices, but not for PCIe devices.  That may lead to misunderstanding
>> that PME poll is only necessary for PCI devices.  So add comments
>> related to PCIe PME poll to make it more clear.
>>
>> The content of comments comes from the changelog of commit:
>>
>> 379021d5c0899fcf9410cae4ca7a59a5a94ca769
>>
>> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>> Signed-off-by: Huang Ying <ying.huang@intel.com>
>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

I applied this to my pci/misc branch as v3.8 material.  Thanks!

>> ---
>>  drivers/pci/pci.c |   28 +++++++++++++++++++---------
>>  1 file changed, 19 insertions(+), 9 deletions(-)
>>
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -1578,15 +1578,25 @@ void pci_pme_active(struct pci_dev *dev,
>>
>>       pci_write_config_word(dev, dev->pm_cap + PCI_PM_CTRL, pmcsr);
>>
>> -     /* PCI (as opposed to PCIe) PME requires that the device have
>> -        its PME# line hooked up correctly. Not all hardware vendors
>> -        do this, so the PME never gets delivered and the device
>> -        remains asleep. The easiest way around this is to
>> -        periodically walk the list of suspended devices and check
>> -        whether any have their PME flag set. The assumption is that
>> -        we'll wake up often enough anyway that this won't be a huge
>> -        hit, and the power savings from the devices will still be a
>> -        win. */
>> +     /*
>> +      * PCI (as opposed to PCIe) PME requires that the device have
>> +      * its PME# line hooked up correctly. Not all hardware vendors
>> +      * do this, so the PME never gets delivered and the device
>> +      * remains asleep. The easiest way around this is to
>> +      * periodically walk the list of suspended devices and check
>> +      * whether any have their PME flag set. The assumption is that
>> +      * we'll wake up often enough anyway that this won't be a huge
>> +      * hit, and the power savings from the devices will still be a
>> +      * win.
>> +      *
>> +      * Although PCIe uses in-band PME message instead of PME# line
>> +      * to report PME, PME does not work for some PCIe devices in
>> +      * reality.  For example, there are devices that set their PME
>> +      * status bits, but don't really bother to send a PME message;
>> +      * there are PCI Express Root Ports that don't bother to
>> +      * trigger interrupts when they receive PME messages from the
>> +      * devices below.  So PME poll is used for PCIe devices too.
>> +      */
>>
>>       if (dev->pme_poll) {
>>               struct pci_pme_device *pme_dev;
>>
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.
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Patch hide | download patch | download mbox

--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1578,15 +1578,25 @@  void pci_pme_active(struct pci_dev *dev,
 
 	pci_write_config_word(dev, dev->pm_cap + PCI_PM_CTRL, pmcsr);
 
-	/* PCI (as opposed to PCIe) PME requires that the device have
-	   its PME# line hooked up correctly. Not all hardware vendors
-	   do this, so the PME never gets delivered and the device
-	   remains asleep. The easiest way around this is to
-	   periodically walk the list of suspended devices and check
-	   whether any have their PME flag set. The assumption is that
-	   we'll wake up often enough anyway that this won't be a huge
-	   hit, and the power savings from the devices will still be a
-	   win. */
+	/*
+	 * PCI (as opposed to PCIe) PME requires that the device have
+	 * its PME# line hooked up correctly. Not all hardware vendors
+	 * do this, so the PME never gets delivered and the device
+	 * remains asleep. The easiest way around this is to
+	 * periodically walk the list of suspended devices and check
+	 * whether any have their PME flag set. The assumption is that
+	 * we'll wake up often enough anyway that this won't be a huge
+	 * hit, and the power savings from the devices will still be a
+	 * win.
+	 *
+	 * Although PCIe uses in-band PME message instead of PME# line
+	 * to report PME, PME does not work for some PCIe devices in
+	 * reality.  For example, there are devices that set their PME
+	 * status bits, but don't really bother to send a PME message;
+	 * there are PCI Express Root Ports that don't bother to
+	 * trigger interrupts when they receive PME messages from the
+	 * devices below.  So PME poll is used for PCIe devices too.
+	 */
 
 	if (dev->pme_poll) {
 		struct pci_pme_device *pme_dev;