linux-kernel - Re: [patch 21/32] NTB/msi: Convert to msi_on_each

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Date:   Tue, 30 Nov 2021 16:28:00 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Marc Zygnier <maz@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Megha Dey <megha.dey@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, linux-pci@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jon Mason <jdmason@...zu.us>,
        Dave Jiang <dave.jiang@...el.com>,
        Allen Hubbe <allenbh@...il.com>, linux-ntb@...glegroups.com,
        linux-s390@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>, x86@...nel.org
Subject: Re: [patch 21/32] NTB/msi: Convert to msi_on_each_desc()

On Tue, Nov 30, 2021 at 08:48:03PM +0100, Thomas Gleixner wrote:
> Logan,
> 
> On Tue, Nov 30 2021 at 12:21, Logan Gunthorpe wrote:
> > On 2021-11-29 5:29 p.m., Thomas Gleixner wrote:
> >> I'm way too tired to come up with a proper solution for that, but that
> >> PCI_IRQ_VIRTUAL has to die ASAP.
> >
> > I'm willing to volunteer a bit of my time to clean this up, but I'd need
> > a bit more direction on what a proper solution would look like. The MSI
> > domain code is far from well documented nor is it easy to understand.
> 
> Fair enough. I'm struggling with finding time to document that properly.
> 
> I've not yet made my mind up what the best way forward for this is, but
> I have a few ideas which I want to explore deeper.

I may have lost the plot in all of these patches, but I thought the
direction was moving toward the msi_domain_alloc_irqs() approach IDXD
demo'd here:

https://lore.kernel.org/kvm/162164243591.261970.3439987543338120797.stgit@djiang5-desk3.ch.intel.com/

I'd expect all the descriptor handling code in drivers/ntb/msi.c to
get wrapped in an irq_chip instead of inserting a single-use callback
to the pci core code's implementation:

void __pci_write_msi_msg(struct msi_desc *entry, struct msi_msg *msg)
{
        if (entry->write_msi_msg)
                entry->write_msi_msg(entry, entry->write_msi_msg_data);

If this doesn't become an irq_chip what other way is there to properly
program the addr/data pair as drivers/ntb/msi.c is doing?

Jason