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

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Date:   Wed, 9 Dec 2020 11:17:56 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jerry Snitselaar <jsnitsel@...hat.com>
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 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