Unable to allocate PCIe MSI vector irqs

[saikat mondal]

Sir,

I have a serious issue with this function pci_alloc_irq_vectors. 

So what happens when I'm requesting to allocate 4 numbers of irqs it always return one irq vector, nvec = 1.

I tried with other flag MSIX also it returns one. That's why I'm no able register my other isr_handler as well.

Sir how to resolve it.

#in attached file line number 144

[Anil Kumar Pugalia]

It may not be supported by the device, itself. Check its datasheet.

Regards
Anil

Passion: http://sysplay.in (Playing with Systems)

saikat mondal wrote on 24/07/20 4:23 pm:

--
You received this message because you are subscribed to the Google Groups "SysPlay's Inside Linux" group.
To unsubscribe from this group and stop receiving emails from it, send an email to inside_linux...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/inside_linux/CABY%2BX5%2BbY%2BAopm00JNizZw_ZufmkK_5efnqoHiai5LeNqOicww%40mail.gmail.com.

[Anil Kumar Pugalia]

It may not be supported by the device itself. Check its datasheet.

Regards
Anil

Passion: http://sysplay.in (Playing with Systems)

saikat mondal wrote on 24/07/20 4:23 pm:

Sir,

[saikat mondal]

Hello , the issue was solved....

I checked the same with one quad core CPU ,

It's able to allocate it's working.

To view this discussion on the web visit https://groups.google.com/d/msgid/inside_linux/95616a4a-752a-a61e-e08f-bd3c0945f552%40sarika-pugs.com.

[Aijaz Baig]

Amazing

Could you please elaborate as to why moving to a quad-core machine solved the issue? Is it because uniprocessor (UP) systems do not have an APIC?

Anil, do you have something to add to this? Most web searches for MSI on uniprocessor systems are stressing that "LAPIC  needs to be enabled for MSI(X) to work even on UP systems". Why do we need that? Is it specified in the PCIe spec that it requires an APIC for MSI to work?

If that is the case why is the Linux Kernel not being upfront in this case about this? That this system will not support MSI as it is a UP?

Keen to hear your thoughts

To view this discussion on the web visit https://groups.google.com/d/msgid/inside_linux/CABY%2BX5LbfWfX7SsuMGrUiMLSThNo6FNjP2MDJSGHvbAKoc4L3g%40mail.gmail.com.

--

Best Regards,

Aijaz Baig

[Anil Kumar Pugalia]

Did your board w/ uniprocessor not have APIC?

Regards
Anil

Passion: http://sysplay.in (Playing with Systems)

Aijaz Baig wrote on 02/08/20 3:12 pm:

To view this discussion on the web visit https://groups.google.com/d/msgid/inside_linux/CAHB2L%2BfTBNExxRygLxGuTVDBR52jFEVo%3DkBkY%3DVYX7ZHajyRvQ%40mail.gmail.com.