Re: [dpdk-dev] [RFC PATCH v3 2/3] eal: add mask and unmask interrupt APIs

[Jerin Jacob Kollanukkaran <jerinj@marvell.com>]

> > I think, it vary from the perspective of IRQ Chip(or controller) vs
> > NIC
> > register(Source) PoV.
> > Since the API starts from rte_intr_* it is more of controller so _ack_
> > make sense Other reason for ack:
> > 1) It will enforce that it needs to be called form ISR
> > 2) It would be have been really correct to unmask if VFIO+MSIx+Linux
> > supports it
> > 3) if it is ack, no need to add unmask counterpart, the _mask_ API
> >
> 
> Just curious, what you mean by irq controller? Ack/mask/unmask PIOs all go

Programmable Interrupt Controller. Like Intel 8259A, GIC from ARM etc
The drivers in linux/drivers/irqchip/

> to the NIC. It is the NIC that asserts/de-asserts irq..
> 
> > >
> > > Besides the name, are we agreeing that we want these?
> > > - Unmask if INTx
> >
> > Yes
> >
> > > - Nothing if MSI/MSI-X
> > Yes for MSI over VFIO
> > No for MSI over UIO/igb_uio
> >
> 
> I guess I was not clear. For MSI/MSI-X, we do not want to do mask/unmask
> regardless of vfio-pci/igb_uio.  Below is my comment about
> linux/windows/freebsd from an earlier email. Do you disagree? I am sure
> there are plenty of kernel NIC driver guys here. Please correct me if I am
> mistaken...


For some reason, igb_uio kernel driver mask the interrupt for MSIx.
We need to ack or unmask if needs to work with MSIX + IGB_UIO.

See 
pci_uio_alloc_resource()
        if (dev->kdrv == RTE_KDRV_IGB_UIO)
                dev->intr_handle.type = RTE_INTR_HANDLE_UIO; 
        else {
                dev->intr_handle.type = RTE_INTR_HANDLE_UIO_INTX;

igbuio_pci_irqcontrol() for masking in kernel.

So it is more of making inline with igb_uio kernel driver AND not break
The existing drivers which was using rte_intr_enable in ISR with MSIX+IGB_UIO

I do agree with that for edge trigged interrupt mask may not require from kernel.
But I am not sure why it is added in igb_uio kernel driver. May  be it is just legacy.
Anyway this wont change schematics, when igb_uio kenrel fixed then the counter
Part can be changed in rte_intr_ack(). Ie. it is transparent to drivers.

> 
> > I don't  have very strong opinion unmask vs ack. I prefer to have ack
> > due the reasons stated above.
> > If you really have strong opinion on using unmask, we will stick with
> > that to make forward progress.
> > Let us know.
> >
> 
> I have no strong opinion either.

OK. Lets stick with rte_intr_ack().

> 
> Thanks..
> -Hyong