Re: [Qemu-devel] [PATCH v2 2/2] PCI-e device multi-function hot-add support

[Cao jin <caoj.fnst@cn.fujitsu.com>]

Hi Alex

On 09/22/2015 02:00 AM, Alex Williamson wrote:
>
> Please use different subjects that uniquely identify what each patch
> does, don't simply re-use the subject for the cover patch on each.

OK, will change it in next version.
>
> On Wed, 2015-09-16 at 10:02 +0800, Cao jin wrote:
>> In case user regret when hot-add multi-function, we should roll back,
>> device_del the function added but still not worked.
>>
>> Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
>> ---
>>   hw/pci/pcie.c | 18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>>
>> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
>> index 89bf61b..497f390 100644
>> --- a/hw/pci/pcie.c
>> +++ b/hw/pci/pcie.c
>> @@ -265,9 +265,27 @@ void pcie_cap_slot_hot_unplug_request_cb(HotplugHandler *hotplug_dev,
>>                                            DeviceState *dev, Error **errp)
>>   {
>>       uint8_t *exp_cap;
>> +    PCIDevice *pci_dev = PCI_DEVICE(dev);
>> +    PCIBus *bus = pci_dev->bus;
>>
>>       pcie_cap_slot_hotplug_common(PCI_DEVICE(hotplug_dev), dev, &exp_cap, errp);
>>
>> +    /* handle the condition: user hot-add multi function, but regret before
>> +     * finish it, and want to delete the added but not worked function. Fake
>> +     * the condition: the slot is polulated, power indicator is off and power
>> +     * controller is off, so device can be detached when OS write config space.
>> +     */
>> +    if (PCI_FUNC(pci_dev->devfn) > 0 &&
>> +            bus->devices[PCI_DEVFN(0, 0)] == NULL) {
>> +        pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTSTA,
>> +                PCI_EXP_SLTSTA_PDS);
>
> AFAICT, we're only setting this to make pcie_cap_slot_write_config()
> consider this device for being unplugged.  Would it not be cleaner to
> flag the device as unexposed to the guest and also use that flag to
> prevent config reads and writes to the device until function 0 is
> populated, so we know that the guest hasn't interacted with the device?
>
Yes, set PDS bit here, for the purpose that fake the unplug condition in 
pcie_cap_slot_write_config(), which means, let guest decide when to 
unplug device. So I think setting PDS bit here is necessary, am I right?

I am not quite clear about "flag device as unexposed", does the flag 
means PCI_EXP_SLTSTA_PDS bit, or anything else? Could you give more 
hints about it?
>> +
>> +        pcie_cap_slot_event(PCI_DEVICE(hotplug_dev),
>> +                PCI_EXP_HP_EV_PDC | PCI_EXP_HP_EV_ABP);
>
> Why do we need to test both vs just ABP, which is signaled in the
> existing patch below?
>

Test the two hotplug event, yes, ABP is enough for device_del. will 
remove PDC in next version.

>> +
>> +        return;
>> +    }
>> +
>>       pcie_cap_slot_push_attention_button(PCI_DEVICE(hotplug_dev));
>>   }
>>
>
>
> .
>

-- 
Yours Sincerely,

Cao Jin