linux-kernel - Re: [PATCH v2 3/7] iommu/arm-smmu: Add dependency on io-pgtable format modules

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Message-ID: <d2af5f0b1543ad374bc419507455a3cf@codeaurora.org>
Date:   Wed, 23 Dec 2020 07:10:56 -0800
From:   isaacm@...eaurora.org
To:     Robin Murphy <robin.murphy@....com>
Cc:     iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        freedreno@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, pratikp@...eaurora.org,
        joro@...tes.org, kernel-team@...roid.com, will@...nel.org,
        pdaly@...eaurora.org
Subject: Re: [PATCH v2 3/7] iommu/arm-smmu: Add dependency on io-pgtable
 format modules

On 2020-12-23 05:05, Robin Murphy wrote:
> On 2020-12-22 19:49, isaacm@...eaurora.org wrote:
>> On 2020-12-22 11:27, Robin Murphy wrote:
>>> On 2020-12-22 00:44, Isaac J. Manjarres wrote:
>>>> The SMMU driver depends on the availability of the ARM LPAE and
>>>> ARM V7S io-pgtable format code to work properly. In preparation
>>> 
>>> Nit: we don't really depend on v7s - we *can* use it if it's
>>> available, address constraints are suitable, and the SMMU
>>> implementation actually supports it (many don't), but we can still
>>> quite happily not use it even so. LPAE is mandatory in the
>>> architecture so that's our only hard requirement, embodied in the
>>> kconfig select.
>>> 
>>> This does mean there may technically still be a corner case involving
>>> ARM_SMMU=y and IO_PGTABLE_ARM_V7S=m, but at worst it's now a runtime
>>> failure rather than a build error, so unless and until anyone
>>> demonstrates that it actually matters I don't feel particularly
>>> inclined to give it much thought.
>>> 
>>> Robin.
>>> 
>> Okay, I'll fix up the commit message, as well as the code, so that it
>> only depends on io-pgtable-arm.
> 
> Well, IIUC it would make sense to keep the softdep for when the v7s
> module *is* present; I just wanted to clarify that it's more of a
> nice-to-have rather than a necessity.
> 
> Robin.
> 
Understood, I will keep it there and reword the commit msg. I just tried 
it out in an environment
where the io-pgtable-arm-v7s module isn't present, and I didn't see any
warnings or error messages, and the SMMU driver module was loaded 
properly,
so yes, it's good to have it.

Thanks,
Isaac
>> Thanks,
>> Isaac
>>>> for having the io-pgtable formats as modules, add a "pre"
>>>> dependency with MODULE_SOFTDEP() to ensure that the io-pgtable
>>>> format modules are loaded before loading the ARM SMMU driver module.
>>>> 
>>>> Signed-off-by: Isaac J. Manjarres <isaacm@...eaurora.org>
>>>> ---
>>>>   drivers/iommu/arm/arm-smmu/arm-smmu.c | 1 +
>>>>   1 file changed, 1 insertion(+)
>>>> 
>>>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c 
>>>> b/drivers/iommu/arm/arm-smmu/arm-smmu.c
>>>> index d8c6bfd..a72649f 100644
>>>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
>>>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
>>>> @@ -2351,3 +2351,4 @@ MODULE_DESCRIPTION("IOMMU API for ARM 
>>>> architected SMMU implementations");
>>>>   MODULE_AUTHOR("Will Deacon <will@...nel.org>");
>>>>   MODULE_ALIAS("platform:arm-smmu");
>>>>   MODULE_LICENSE("GPL v2");
>>>> +MODULE_SOFTDEP("pre: io-pgtable-arm io-pgtable-arm-v7s");
>>>> 
>>> 
>>> _______________________________________________
>>> linux-arm-kernel mailing list
>>> linux-arm-kernel@...ts.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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