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

[Liviu Dudau]

On Tue, Sep 19, 2017 at 10:07:58AM +0300, 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.

This is on arm64, on the Arm Juno board.

> 
> > 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.

drm-next. :)
Looks like things have move forward since I've made the patch before
LPC, will update and resend.

Best regards,
Liviu

> 
> > @@ -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
> 

-- 
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