linux-kernel - Re: [PATCH v2] iommu/ipmmu-vmsa: Do not replace bus IOMMU ops on driver init.

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Message-ID: <938d213c-f207-218e-554f-08035eaa1e6d@arm.com>
Date:   Fri, 13 Oct 2017 16:48:45 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Liviu Dudau <Liviu.Dudau@....com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Magnus Damm <damm+renesas@...nsource.se>,
        LKML <linux-kernel@...r.kernel.org>,
        IOMMU ML <iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH v2] iommu/ipmmu-vmsa: Do not replace bus IOMMU ops on
 driver init.

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@....com>
> Cc: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.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@...asonboard.com>");
>