linux-kernel - Re: [PATCH] iommu: Add Kconfig help text for IOMMU

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Message-ID: <20230506150741.2e3d2dcc@jacob-builder>
Date:   Sat, 6 May 2023 15:07:41 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
        Jason Gunthorpe <jgg@...dia.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>, Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH] iommu: Add Kconfig help text for IOMMU_SVA

Hi Linus,

On Sat, 6 May 2023 08:43:08 -0700, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:

> On Sat, May 6, 2023 at 6:27 AM Jacob Pan <jacob.jun.pan@...ux.intel.com>
> wrote:
> >
> > Shared Virtual Addressing (SVA) is not immediately intuitive to people
> > who work outside IOMMU subsystem, add some explanation to make it less
> > opaque.  
> 
> So the patch has at least two problems.
> 
> The first is that you corrupted the SPDX line.
> 
Sorry, my mistake. Will not try sending patches before fully waking up.

> But the second is that the change from
> 
> -       bool
> +       bool "Shared Virtual Addressing"
> 
> means that now Kconfig *asks* about this thing, which was never the
> intent. The other Kconfig options that need it all do a
> 
>         select IOMMU_SVA
> 
> to get it picked.
> 
> I suspect that's why it then causes errors - because now the test
> robot can enable the option even in situations where it makes no sense
> and doesn't work.
> 
> So no, it's not that the option needs a help entry that can be queried
> at Kconfig time. It's that the option needs a name that makes sense
> and isn't some random jumble of letters that is only understandable to
> people who already know exactly what it is.
Right, how about IOMMU_SHARING_CPU_PGTABLE?

Since this is more of a one-sided relationship where IOMMU walks CPU page
tables.


Thanks,

Jacob