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

    On 19/09/17 08:07, Laurent Pinchart wrote:
    > 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.

    Yes, that used to be the problem, but since IPMMU uses the generic
    bindings and iommu_device_register(), it should now benefit from client
    probe-deferral even when it doesn't support of_xlate().

    Robin.

    >> 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@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 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@ideasonboard.com>");
    >

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