linux-kernel - Re: [GIT PULL] IOMMU fix for 5.10 (-final)

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Date:   Wed, 9 Dec 2020 12:23:06 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Will Deacon <will@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Robin Murphy <robin.murphy@....com>,
        iommu <iommu@...ts.linux-foundation.org>
Subject: Re: [GIT PULL] IOMMU fix for 5.10 (-final)

On Wed, Dec 9, 2020 at 12:18 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Wed, Dec 9, 2020 at 11:12 AM Jerry Snitselaar <jsnitsel@...hat.com> wrote:
> >
> > Since the field in the device table entry format expects it to be n
> > where there are 2^n entries in the table I guess it should be:
> >
> > #define DTE_IRQ_TABLE_LEN 9
> > #define MAX_IRQS_PER_TABLE (1 << DTE_IRQ_TABLE_LEN)
>
> No, that "DTE_IRQ_TABLE_LEN" is not the size shift - it's the size
> shift value in that DTE field, which is shifted up by 1.
>
> That's why the current code does that
>
>    #define DTE_IRQ_TABLE_LEN       (9ULL << 1)
>
> there..
>
> Which was why I suggested that new #define that is the *actual* shift
> value, and then the DTE thing and the MAX_IRQS_PER_TABLE values would
> depend on that.
>
>            Linus
>

Yes, when I read it my head was translating it as setting them both to
512 and then
I forgot that it gets shifted over 1. Which considering I was the once
who noticed the
original problem  of it still being 8 was a nice brain fart. This
should be fixed like you suggest.