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SubjectRe: [PATCH v2] iommu/ipmmu-vmsa: Do not replace bus IOMMU ops on driver init.
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Hi Joerg,

On 20/09/17 15:13, Liviu Dudau wrote:
> If the IPMMU driver is compiled in the kernel it will replace the
> platform bus IOMMU ops on running the ipmmu_init() function, regardless
> if there is any IPMMU hardware present or not. This screws up systems
> that just want to build a generic kernel that runs on multiple platforms
> and use a different IOMMU implementation.
>
> Move the bus_set_iommu() call at the end of the ipmmu_probe() function
> when we know that hardware is present. With current IOMMU framework it
> should be safe (at least for OF case).
>
> Now that the ipmmu_init() and ipmmu_exit() functions are simple calls to
> platform_driver_register() and platform_driver_unregister(), replace
> them with the module_platform_driver() macro call.

Are you OK with taking this patch as a fix for 4.14, or would you rather
have something that can safely backport past 4.12 without implicit
dependencies? This is a config/link-order dependent thing that's been
lurking since the beginning, but only coming to light now that other
drivers are changing their behaviour, so I don't think there's really a
single Fixes: commit that can be singled out.

Robin.

> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
> Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> ---
> drivers/iommu/ipmmu-vmsa.c | 29 +++++------------------------
> 1 file changed, 5 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/iommu/ipmmu-vmsa.c b/drivers/iommu/ipmmu-vmsa.c
> index 195d6e93ac718..31912997bffdf 100644
> --- a/drivers/iommu/ipmmu-vmsa.c
> +++ b/drivers/iommu/ipmmu-vmsa.c
> @@ -966,10 +966,11 @@ static int ipmmu_probe(struct platform_device *pdev)
> return ret;
>
> /*
> - * We can't create the ARM mapping here as it requires the bus to have
> - * an IOMMU, which only happens when bus_set_iommu() is called in
> - * ipmmu_init() after the probe function returns.
> + * Now that we have validated the presence of the hardware, set
> + * the bus IOMMU ops to enable future domain and device setup.
> */
> + if (!iommu_present(&platform_bus_type))
> + bus_set_iommu(&platform_bus_type, &ipmmu_ops);
>
> platform_set_drvdata(pdev, mmu);
>
> @@ -1006,27 +1007,7 @@ static struct platform_driver ipmmu_driver = {
> .remove = ipmmu_remove,
> };
>
> -static int __init ipmmu_init(void)
> -{
> - int ret;
> -
> - ret = platform_driver_register(&ipmmu_driver);
> - if (ret < 0)
> - return ret;
> -
> - if (!iommu_present(&platform_bus_type))
> - bus_set_iommu(&platform_bus_type, &ipmmu_ops);
> -
> - return 0;
> -}
> -
> -static void __exit ipmmu_exit(void)
> -{
> - return platform_driver_unregister(&ipmmu_driver);
> -}
> -
> -subsys_initcall(ipmmu_init);
> -module_exit(ipmmu_exit);
> +module_platform_driver(ipmmu_driver);
>
> MODULE_DESCRIPTION("IOMMU API for Renesas VMSA-compatible IPMMU");
> MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@ideasonboard.com>");
>

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