Re: [PATCH 1/2] pcie: Don't try triggering a LSI when not defined

[Daniel Henrique Barboza <danielhb413@gmail.com>]

On 3/24/22 10:47, Frederic Barrat wrote:
> 
> 
> On 24/03/2022 14:07, Daniel Henrique Barboza wrote:
>>
>>
>> On 3/21/22 12:33, Frederic Barrat wrote:
>>> This patch skips [de]asserting a LSI interrupt if the device doesn't
>>> have any LSI defined. Doing so would trigger an assert in
>>> pci_irq_handler().
>>>
>>> The PCIE root port implementation in qemu requests a LSI (INTA), but a
>>> subclass may want to change that behavior since it's a valid
>>> configuration. For example on the POWER8/POWER9/POWER10 systems, the
>>> root bridge doesn't request any LSI.
>>>
>>> Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
>>> ---
>>
>> I assume that it's easier to handle just the codepaths that powernv PHBs uses
>> rather than handling all instances where pci_irq_handler() would be asserting
>> without LSIs.
> 
> 
> The real reason is that the LSI is added when we realize the TYPE_PCIE_ROOT_PORT object. See rp_realize(). So I'm only trying to fix the code paths that can be called from a subclass of TYPE_PCIE_ROOT_PORT which would choose to override the "interrupt pin" setting in the config space. I believe they are all covered by this patch.
> The assert() in pci_irq_handler() is there for a reason and I don't want to mess with that.


Yes, handling this situation inside pci_irq_handler() would require changing the
"assert(0 <= irq_num && irq_num < PCI_NUM_PINS)" assert or doing some sanity before
it to avoid the trigger.

Since this is a common code used everywhere we're better of doing minimalist changes
as you're doing. We can reevaluate this design if more machines/devices start to get
in the same situation we have now with powernv PHBs.


Daniel

> 
>    Fred
> 
> 
>>
>>
>> Patch LGTM. Small nits below:
>>
>>>   hw/pci/pcie.c     | 8 ++++++--
>>>   hw/pci/pcie_aer.c | 4 +++-
>>>   2 files changed, 9 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
>>> index 67a5d67372..71c5194b80 100644
>>> --- a/hw/pci/pcie.c
>>> +++ b/hw/pci/pcie.c
>>> @@ -354,7 +354,9 @@ static void hotplug_event_notify(PCIDevice *dev)
>>>       } else if (msi_enabled(dev)) {
>>>           msi_notify(dev, pcie_cap_flags_get_vector(dev));
>>>       } else {
>>> -        pci_set_irq(dev, dev->exp.hpev_notified);
>>> +        if (pci_intx(dev) != -1) {
>>> +            pci_set_irq(dev, dev->exp.hpev_notified);
>>> +        }
>>
>>
>> Since you're not doing anything unless the condition is met, you can use 'else if'
>> like it's done in the other conditionals:
>>
>>
>>      if (msix_enabled(dev)) {
>>          msix_notify(dev, pcie_cap_flags_get_vector(dev));
>>      } else if (msi_enabled(dev)) {
>>          msi_notify(dev, pcie_cap_flags_get_vector(dev));
>>      } else if (pci_intx(dev) != -1) {
>>          pci_set_irq(dev, dev->exp.hpev_notified);
>>      }
>>
>>
>>
>>>       }
>>>   }
>>> @@ -362,7 +364,9 @@ static void hotplug_event_clear(PCIDevice *dev)
>>>   {
>>>       hotplug_event_update_event_status(dev);
>>>       if (!msix_enabled(dev) && !msi_enabled(dev) && !dev->exp.hpev_notified) {
>>> -        pci_irq_deassert(dev);
>>> +        if (pci_intx(dev) != -1) {
>>> +            pci_irq_deassert(dev);
>>> +        }
>>>       }
>>
>> Similar comment here:
>>
>>      if (!msix_enabled(dev) && !msi_enabled(dev) && !dev->exp.hpev_notified &&
>>          pci_intx(dev) != -1) {
>>          pci_irq_deassert(dev);
>>      }
>>
>>
>>
>>>   }
>>> diff --git a/hw/pci/pcie_aer.c b/hw/pci/pcie_aer.c
>>> index e1a8a88c8c..d936bfca20 100644
>>> --- a/hw/pci/pcie_aer.c
>>> +++ b/hw/pci/pcie_aer.c
>>> @@ -291,7 +291,9 @@ static void pcie_aer_root_notify(PCIDevice *dev)
>>>       } else if (msi_enabled(dev)) {
>>>           msi_notify(dev, pcie_aer_root_get_vector(dev));
>>>       } else {
>>> -        pci_irq_assert(dev);
>>> +        if (pci_intx(dev) != -1) {
>>> +            pci_irq_assert(dev);
>>> +        }
>>
>>
>> And here:
>>
>>      if (msix_enabled(dev)) {
>>          msix_notify(dev, pcie_aer_root_get_vector(dev));
>>      } else if (msi_enabled(dev)) {
>>          msi_notify(dev, pcie_aer_root_get_vector(dev));
>>      } else if (pci_intx(dev) != -1) {
>>          pci_irq_assert(dev);
>>      }
>>
>>
>>
>> Thanks,
>>
>>
>> Daniel
>>
>>>       }
>>>   }