[PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE_DART invisible

[PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE_DART invisible

[Geert Uytterhoeven]

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@glider.be>
---
Should IOMMU_IO_PGTABLE_LPAE and IOMMU_IO_PGTABLE_ARMV7S be made
invisible, too?
Are there users that do not select them?
---
 drivers/iommu/Kconfig | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index dc5f7a156ff5ec73..f1affca6022e0a54 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -68,16 +68,13 @@ config IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
 	  If unsure, say N here.
 
 config IOMMU_IO_PGTABLE_DART
-	bool "Apple DART Formats"
+	bool
 	select IOMMU_IO_PGTABLE
-	depends on ARM64 || (COMPILE_TEST && !GENERIC_ATOMIC64)
 	help
 	  Enable support for the Apple DART pagetable formats. These include
 	  the t8020 and t6000/t8110 DART formats used in Apple M1/M2 family
 	  SoCs.
 
-	  If unsure, say N here.
-
 endmenu
 
 config IOMMU_DEBUGFS
-- 
2.25.1


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Re: [PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE_DART invisible

[Robin Murphy]

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@glider.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.

Thanks,
Robin.

> ---
>   drivers/iommu/Kconfig | 5 +----
>   1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index dc5f7a156ff5ec73..f1affca6022e0a54 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -68,16 +68,13 @@ config IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
>   	  If unsure, say N here.
>   
>   config IOMMU_IO_PGTABLE_DART
> -	bool "Apple DART Formats"
> +	bool
>   	select IOMMU_IO_PGTABLE
> -	depends on ARM64 || (COMPILE_TEST && !GENERIC_ATOMIC64)
>   	help
>   	  Enable support for the Apple DART pagetable formats. These include
>   	  the t8020 and t6000/t8110 DART formats used in Apple M1/M2 family
>   	  SoCs.
>   
> -	  If unsure, say N here.
> -
>   endmenu
>   
>   config IOMMU_DEBUGFS

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Re: [PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE_DART invisible

[Geert Uytterhoeven]

Hi Robin,

On Tue, Sep 27, 2022 at 4:15 PM Robin Murphy <robin.murphy@arm.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@glider.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

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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Re: [PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE_DART invisible

[Robin Murphy]

On 2022-09-27 15:48, Geert Uytterhoeven wrote:
> Hi Robin,
> 
> On Tue, Sep 27, 2022 at 4:15 PM Robin Murphy <robin.murphy@arm.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@glider.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.

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Re: [PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE_DART invisible

[Geert Uytterhoeven]

Hi Robin,

On Tue, Sep 27, 2022 at 5:09 PM Robin Murphy <robin.murphy@arm.com> wrote:
> On 2022-09-27 15:48, Geert Uytterhoeven wrote:
> > On Tue, Sep 27, 2022 at 4:15 PM Robin Murphy <robin.murphy@arm.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@glider.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?

Agreed.

> 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 :/

So perhaps the visibility of IOMMU_IO_PGTABLE_LPAE and
IOMMU_IO_PGTABLE_ARMV7S should depend on COMPILE_TEST?
Normal users would still get it through select when needed.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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Re: [PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE_DART invisible

[Robin Murphy]

On 2022-09-27 16:29, Geert Uytterhoeven wrote:
> Hi Robin,
> 
> On Tue, Sep 27, 2022 at 5:09 PM Robin Murphy <robin.murphy@arm.com> wrote:
>> On 2022-09-27 15:48, Geert Uytterhoeven wrote:
>>> On Tue, Sep 27, 2022 at 4:15 PM Robin Murphy <robin.murphy@arm.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@glider.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?
> 
> Agreed.
> 
>> 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 :/
> 
> So perhaps the visibility of IOMMU_IO_PGTABLE_LPAE and
> IOMMU_IO_PGTABLE_ARMV7S should depend on COMPILE_TEST?
> Normal users would still get it through select when needed.

As I say those still offer functionality beyond compile-testing, but now 
you've got me suspecting that it's already suboptimal that one has to 
enable the format to make the self-test option appear... Perhaps what we 
want is a separate master option to enable io-pgtable self-tests in 
general, then rejig the rest around that.

Of course the self-tests would be even more useful if the harness was at 
the level of the core io-pgtable API so it could cover new formats 
automatically as long as they provide the configuration parameters, but 
that's a separate matter for someone with sufficient free time and 
enthusiasm :)

Cheers,
Robin.

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Re: [PATCH] iommu/io-pgtable: Make IOMMU_IO_PGTABLE_DART invisible

[Geert Uytterhoeven]

Hi Robin,

On Tue, Sep 27, 2022 at 5:50 PM Robin Murphy <robin.murphy@arm.com> wrote:
> On 2022-09-27 16:29, Geert Uytterhoeven wrote:
> > On Tue, Sep 27, 2022 at 5:09 PM Robin Murphy <robin.murphy@arm.com> wrote:
> >> On 2022-09-27 15:48, Geert Uytterhoeven wrote:
> >>> On Tue, Sep 27, 2022 at 4:15 PM Robin Murphy <robin.murphy@arm.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@glider.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?
> >
> > Agreed.
> >
> >> 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 :/
> >
> > So perhaps the visibility of IOMMU_IO_PGTABLE_LPAE and
> > IOMMU_IO_PGTABLE_ARMV7S should depend on COMPILE_TEST?
> > Normal users would still get it through select when needed.
>
> As I say those still offer functionality beyond compile-testing, but now
> you've got me suspecting that it's already suboptimal that one has to
> enable the format to make the self-test option appear... Perhaps what we

IMHO that's the only sensible thing to do: you want to have the option
to enable (preferably modular) tests for the functionality you have
enabled in your product, so you can run the tests when needed.

> want is a separate master option to enable io-pgtable self-tests in
> general, then rejig the rest around that.

IMHO you do not want a master test option that suddenly enables
lots of functionality you do not need in your product.

> Of course the self-tests would be even more useful if the harness was at
> the level of the core io-pgtable API so it could cover new formats
> automatically as long as they provide the configuration parameters, but
> that's a separate matter for someone with sufficient free time and
> enthusiasm :)

OK, I will shut up ;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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