linux-kernel - Re: [PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE

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Date:   Tue, 27 Sep 2022 16:09:21 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Sven Peter <sven@...npeter.dev>, Janne Grunau <j@...nau.net>,
        Hector Martin <marcan@...can.st>, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE_DART invisible

On 2022-09-27 15:48, Geert Uytterhoeven wrote:
> Hi Robin,
> 
> On Tue, Sep 27, 2022 at 4:15 PM Robin Murphy <robin.murphy@....com> wrote:
>> On 2022-09-27 14:36, Geert Uytterhoeven wrote:
>>> There is no point in asking the user about both "Apple DART Formats" and
>>> "Apple DART IOMMU Support", as the former is useless without the latter,
>>> and the latter auto-selects the former.
>>>
>>> Fixes: 745ef1092bcfcf3b ("iommu/io-pgtable: Move Apple DART support to its own file")
>>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>>> ---
>>> Should IOMMU_IO_PGTABLE_LPAE and IOMMU_IO_PGTABLE_ARMV7S be made
>>> invisible, too?
>>> Are there users that do not select them?
>>
>> The aim was for formats to be independently selectable for COMPILE_TEST
>> coverage. The Arm formats are manually selectable for the sake of their
>> runtime self-tests, which are self-contained, but since DART format
>> doesn't do anything by itself I'd agree there's no need to prompt when
>> !COMPILE_TEST here.
> 
> IOMMU_IO_PGTABLE_LPAE and IOMMU_IO_PGTABLE_ARMV7S are
> selected by other symbols that can be enabled when compile-testing, so
> the tests can still be enabled in those cases, too

Sure, but when you want to compile-test a thing, what would you rather 
do: enable the thing, or go hunting to find some other thing that 
happens to select the thing you actually want, then potentially have to 
figure out *that* thing's dependencies, and so on?

Coverage isn't solely about whether it's technically possible to ever 
reach somewhere at all, it's just as much about how easily and/or often 
you can get there in practice. I don't see who benefits from making 
COMPILE_TEST harder to use :/

Thanks,
Robin.