Re: PCIe MSI address is not written at pci_enable_msi_range call

[Marc Zyngier]

On 12/07/16 10:11, Bharat Kumar Gogada wrote:
>> Subject: Re: PCIe MSI address is not written at pci_enable_msi_range call
>>
>> On 11/07/16 11:51, Bharat Kumar Gogada wrote:
>>>>> Hi Marc,
>>>>>
>>>>> Thanks for the reply.
>>>>>
>>>>> From PCIe Spec:
>>>>> MSI Enable Bit:
>>>>> If 1 and the MSI-X Enable bit in the MSI-X Message Control register
>>>>> (see Section 6.8.2.3) is 0, the function is permitted to use MSI to
>>>>> request service and is prohibited from using its INTx# pin.
>>>>>
>>>>> From Endpoint perspective, MSI Enable = 1 indicates MSI can be used
>>>> which means MSI address and data fields are available/programmed.
>>>>>
>>>>> In our SoC whenever MSI Enable goes from 0 --> 1 the hardware
>>>>> latches
>>>> onto MSI address and MSI data values.
>>>>>
>>>>> With current MSI implementation in kernel, our SoC is latching on to
>>>> incorrect address and data values, as address/data
>>>>> are updated much later than MSI Enable bit.
>>>>
>>>> Interesting. It looks like we're doing something wrong in the MSI flow.
>>>> Can you confirm that this is limited to MSI and doesn't affect MSI-X?
>>>>
>>> I think it's the same issue irrespective of MSI or MSI-X as we are
>>> enabling these interrupts before providing the  vectors.
>>>
>>> So we always have a hole when MSI/MSI-X is 1, and software driver has
>>> not registered the irq, and End Point may raise an interrupt (may be
>>> due to error) in this point of time.
>>
>> Looking at the MSI-X part of the code, there is this:
>>
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/pci
>> /msi.c#n764
>>
>> which hints that it may not be possible to do otherwise. Damned if you do,
>> damned if you don't.
>>
> MSI-X might not have problem then, how to resolve the issue with MSI ?

Can you give this patch a go and let me know if that works for you?

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index a080f44..565e2a4 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -1277,6 +1277,8 @@ struct irq_domain *pci_msi_create_irq_domain(struct fwnode_handle *fwnode,
 	if (info->flags & MSI_FLAG_USE_DEF_CHIP_OPS)
 		pci_msi_domain_update_chip_ops(info);
 
+	info->flags |= MSI_FLAG_ACTIVATE_EARLY;
+
 	domain = msi_create_irq_domain(fwnode, info, parent);
 	if (!domain)
 		return NULL;
diff --git a/include/linux/msi.h b/include/linux/msi.h
index 8b425c6..513b7c7 100644
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -270,6 +270,8 @@ enum {
 	MSI_FLAG_MULTI_PCI_MSI		= (1 << 3),
 	/* Support PCI MSIX interrupts */
 	MSI_FLAG_PCI_MSIX		= (1 << 4),
+	/* Needs early activate, required for PCI */
+	MSI_FLAG_ACTIVATE_EARLY		= (1 << 5),
 };
 
 int msi_domain_set_affinity(struct irq_data *data, const struct cpumask *mask,
diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
index 38e89ce..4ed2cca 100644
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -361,6 +361,13 @@ int msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev,
 		else
 			dev_dbg(dev, "irq [%d-%d] for MSI\n",
 				virq, virq + desc->nvec_used - 1);
+
+		if (info->flags & MSI_FLAG_ACTIVATE_EARLY) {
+			struct irq_data *irq_data;
+
+			irq_data = irq_domain_get_irq_data(domain, desc->irq);
+			irq_domain_activate_irq(irq_data);
+		}
 	}
 
 	return 0;


Thanks,

	M.

-- 
Jazz is not dead. It just smells funny...