Re: [PATCH] drivers/pci/hotplug: Handle presence detection change properly

[Gavin Shan <gwshan@linux.vnet.ibm.com>]

On Tue, Dec 20, 2016 at 10:37:09AM +0100, Greg KH wrote:
>On Tue, Dec 20, 2016 at 05:49:33PM +1100, Gavin Shan wrote:
>> The surprise hotplug is driven by interrupt in PowerNV PCI hotplug
>> driver. In the interrupt handler, pnv_php_interrupt(), we bail when
>> pnv_pci_get_presence_state() returns zero wrongly. It causes the
>> presence change event is always ignored incorrectly.
>> 
>> This fixes the issue by bailing on error (non-zero value) returned
>> from pnv_pci_get_presence_state().
>> 
>> Fixes: 360aebd85a4 ("drivers/pci/hotplug: Support surprise hotplug in powernv driver")
>> Cc: stable@vger.kernel.org #v4.9+
>> Reported-by: Hank Chang <hankmax0000@gmail.com>
>> Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
>> Tested-by: Willie Liauw <williel@supermicro.com.tw>
>> ---
>>  drivers/pci/hotplug/pnv_php.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/pci/hotplug/pnv_php.c b/drivers/pci/hotplug/pnv_php.c
>> index 56efaf7..38a2309 100644
>> --- a/drivers/pci/hotplug/pnv_php.c
>> +++ b/drivers/pci/hotplug/pnv_php.c
>> @@ -707,8 +707,12 @@ static irqreturn_t pnv_php_interrupt(int irq, void *data)
>>  		added = !!(lsts & PCI_EXP_LNKSTA_DLLLA);
>>  	} else if (sts & PCI_EXP_SLTSTA_PDC) {
>>  		ret = pnv_pci_get_presence_state(php_slot->id, &presence);
>> -		if (!ret)
>> +		if (ret) {
>> +			dev_warn(&pdev->dev, "PCI slot [%s] error %d handling PDC event (0x%04x)\n",
>> +				php_slot->name, ret, sts);
>
>What can a user do with this warning?
>

This warning is to catch developer's attention only. It's very
rare for pnv_pci_get_presence_state() to fail as it simply checks
hardware regiter bit (from Slot Status regsiter in PCIe capability
or PHB's Hotplug Override register) in the skiboot firmware.

User needs to retry the operation (hot-add or hot-remove) when
seeing this warning. Greg, please let me know if below message
is better?

dev_warn(&pdev->dev, "PCI slot [%s] error %d getting presence status on event 0x%04x, to retry the operation.\n",
         php_slot->name, ret, sts);

Thanks,
Gavin