linux-kernel - Re: [PATCH 7/7] iommu/arm-smmu: Allow building as a module

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Date:   Wed, 30 Oct 2019 15:33:26 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Rob Herring <robh@...nel.org>, Will Deacon <will@...nel.org>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH 7/7] iommu/arm-smmu: Allow building as a module

On 30/10/2019 15:22, Rob Herring wrote:
> On Wed, Oct 30, 2019 at 02:51:12PM +0000, Will Deacon wrote:
>> By conditionally dropping support for the legacy binding and exporting
>> the newly introduced 'arm_smmu_impl_init()' function we can allow the
>> ARM SMMU driver to be built as a module.
>>
>> Signed-off-by: Will Deacon <will@...nel.org>
>> ---
>>   drivers/iommu/Kconfig         | 14 ++++++++-
>>   drivers/iommu/arm-smmu-impl.c |  6 ++++
>>   drivers/iommu/arm-smmu.c      | 54 +++++++++++++++++++++--------------
>>   3 files changed, 51 insertions(+), 23 deletions(-)
>>
>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
>> index 7583d47fc4d5..02703f51e533 100644
>> --- a/drivers/iommu/Kconfig
>> +++ b/drivers/iommu/Kconfig
>> @@ -350,7 +350,7 @@ config SPAPR_TCE_IOMMU
>>   
>>   # ARM IOMMU support
>>   config ARM_SMMU
>> -	bool "ARM Ltd. System MMU (SMMU) Support"
>> +	tristate "ARM Ltd. System MMU (SMMU) Support"
>>   	depends on (ARM64 || ARM) && MMU
>>   	select IOMMU_API
>>   	select IOMMU_IO_PGTABLE_LPAE
>> @@ -362,6 +362,18 @@ config ARM_SMMU
>>   	  Say Y here if your SoC includes an IOMMU device implementing
>>   	  the ARM SMMU architecture.
>>   
>> +config ARM_SMMU_LEGACY_DT_BINDINGS
>> +	bool "Support the legacy \"mmu-masters\" devicetree bindings"
> 
> Can't we just remove this now? The only user is Seattle. Is anyone still
> using Seattle AND DT? There's been no real dts change since Feb '16.
> There's a bit of clean-up needed in the Seattle dts files, so I'd like
> to remove them if there's not users.
> 
> If there are users, can't we just make them move to the new binding?
> Yes compatibility, but that really depends on the users caring.

Apparently it's also in the wild on Cavium ThunderX/OcteonTX machines as 
well :(

> I though Calxeda was using this too, but I guess we didn't get that
> finished. We should probably remove that secure mode flag as well.

FWIW the secure quirk still comes in useful every now and then when 
people prototype stuff on 32-bit VExpress, where it turns out an SMMU is 
about the only thing which cares whether you're running Linux in Secure 
mode or not.

Robin.