linux-kernel - Re: [PATCH 2/9] PCI/MSI: Support allocating virtual MSI interrupts

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Message-ID: <20190201192323.GS229773@google.com>
Date:   Fri, 1 Feb 2019 13:23:23 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>, g@...gle.com
Cc:     linux-kernel@...r.kernel.org, linux-ntb@...glegroups.com,
        linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kselftest@...r.kernel.org, Jon Mason <jdmason@...zu.us>,
        Joerg Roedel <joro@...tes.org>,
        Allen Hubbe <allenbh@...il.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Eric Pilmore <epilmore@...aio.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>
Subject: Re: [PATCH 2/9] PCI/MSI: Support allocating virtual MSI interrupts

On Thu, Jan 31, 2019 at 03:52:09PM -0700, Logan Gunthorpe wrote:
> On 2019-01-31 3:39 p.m., Bjorn Helgaas wrote:
> >> diff --git a/include/linux/msi.h b/include/linux/msi.h
> >> index 784fb52b9900..6458ab049852 100644
> >> --- a/include/linux/msi.h
> >> +++ b/include/linux/msi.h
> >> @@ -88,6 +88,7 @@ struct msi_desc {
> >>  				__u8	multi_cap	: 3;
> >>  				__u8	maskbit		: 1;
> >>  				__u8	is_64		: 1;
> >> +				__u8    is_virtual      : 1;
> > 
> > You did the right thing by using the same style as what's already
> > here, but does anybody know why are we using __u8 and __u16 here?
> > 
> > Those typedefs are in include/uapi/asm-generic/int-l64.h, which
> > suggests they're for things exported to user space, but I don't think
> > that's the case here, so I'm wondering if we could someday replace
> > these with u8 and u16.  Obviously that wouldn't be part of *this*
> > series.
> 
> Yes, I was also confused by this. But I always follow the "when-in-rome"
> rule. 

Thanks for following the "when-in-rome" rule.  That seems so obvious
that it wouldn't even need to be written down, but it is often
ignored.

> My understanding is the same as yours is that __u8 should be used
> for userspace compatibility which doesn't apply here. If there is
> consensus on this being wrong, I'd be happy to write a cleanup patch
> that fixes it separate from this series.

That'd be awesome.  There are also a couple more in pci-driver.c that
could be fixed at the same time.

Bjorn