Registering handler/ISR for MSI

[gauthamkrishnan_r]

I'm generating an MSI from Endpoint to Root Complex on T2080. How to register handler and route the MSI to appropriate ISR for an MSI received on Root Complex? I don't use linux or other OS. It's a baremetal driver. @ufedor 

[gauthamkrishnan_r]

How can we do this without using linux function calls? @ufedor @yipingwang 

[yipingwang]

You may have to monitor MSI capability registers for possible arrival of MSI write data, which would then invoke the handler you wish to call.

[gauthamkrishnan_r]

I'm currently polling MSI Status registers periodically to figure out any active interrupts. But reading MSI capability registers makes no sense to me with regard to active interrupts.

[yipingwang]

Could you poll the registers succesfully?
I meant something similar, the sequence is as below:

write memory address in memory address register.
write # messages requested in message control register
write basic data pattern in message data register
Set MSI enable in control register.


Now poll the interrupt status register on the RC side.

[gauthamkrishnan_r]

Yes, I'm able to poll it successfully but looking for a solution replicating generation of virtual interrupt numbers when using linux.

[yipingwang]

I think that will be possible only through linux system call interface.

[yipingwang]

Virtual interrupt numbers and its generation/handling are part of linux interrupt framework.
Why do you want to replicate it.

I think we have two clean options:

1. use linux system calls for interrupt framework and routing to interrupt handler through request_irq()

2. use manual polling of MSI interrupt and call a custom handler to handle the interrupt without involving linux interrupt framework.

This would make things simple.

[yipingwang]

To register handler, pci_enable_msi should be called it will reserve a MSI vector.
After that call request_irq function.

err = pci_enable_msi(my_pci_dev);
err = request_irq(my_pci_dev->irq, irq_handler, 0, "PCI_CARD", NULL);

to reserve multiple vectors, use this:

err = pci_enable_msi_block(my_pci_dev,3);
request_irq(my_pci_dev->irq, irq_handler_0, ...); request_irq(my_pci_dev->irq + 1, irq_handler_1, ...); request_irq(my_pci_dev->irq + 2, irq_handler_2, ...);