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

[Laurent Pinchart]

Hi Liviu,

Thank you for the patch.

On Monday, 18 September 2017 13:04:44 EEST 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).

If I recall correctly the issue is that the IPMMU might be probed after bus 
master devices when using the legacy IOMMU DT integration, which the ipmmu-
vmsa driver does on ARM32. Calling bus_set_iommu() from the probe function 
will then result in some devices losing IOMMU support.

> 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.
> 
> Signed-off-by: Liviu Dudau <Liviu.Dudau@xxxxxxx>
> Cc: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
> ---
>  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 2a38aa15be17d..c60569c74678d 100644
> --- a/drivers/iommu/ipmmu-vmsa.c
> +++ b/drivers/iommu/ipmmu-vmsa.c
> @@ -1055,10 +1055,11 @@ static int ipmmu_probe(struct platform_device *pdev)
> ipmmu_device_reset(mmu);
> 
>  	/*
> -	 * 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);
> 
>  	spin_lock(&ipmmu_devices_lock);
>  	list_add(&mmu->list, &ipmmu_devices);

What branch is this patch based on ? ipmmu_devices_lock isn't in mainline.

> @@ -1100,27 +1101,7 @@ 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@xxxxxxxxxxxxxxxx>");

-- 
Regards,

Laurent Pinchart