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

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Message-ID: <20171121120801.GK5165@e110455-lin.cambridge.arm.com>
Date:   Tue, 21 Nov 2017 12:08:01 +0000
From:   Liviu Dudau <Liviu.Dudau@....com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <damm+renesas@...nsource.se>,
        LKML <linux-kernel@...r.kernel.org>,
        IOMMU ML <iommu@...ts.linux-foundation.org>,
        Shawn Lin <shawn.lin@...k-chips.com>
Subject: Re: [PATCH v2] iommu/ipmmu-vmsa: Do not replace bus IOMMU ops on
 driver init.

On Mon, Nov 20, 2017 at 03:01:44PM -0700, Alex Williamson wrote:
> On Mon, 20 Nov 2017 14:25:14 +0000
> Liviu Dudau <Liviu.Dudau@....com> wrote:
> 
> > On Fri, Oct 13, 2017 at 04:48:45PM +0100, Robin Murphy wrote:
> > > Hi Joerg,  
> > 
> > Hi,
> > 
> > > 
> > > 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.  
> > 
> > Can someone update me on the fate of this patch? Can someone queue it
> > for the next release?
> 
> Sorry, this is another patch that wasn't on my radar while Joerg is out
> on paternity leave.  I didn't follow the replies to Laurent's question
> about ordering and perhaps this plays in to Robin asking about fixes
> for specific kernel versions.  It seems there are some changes
> elsewhere that somehow defer the ordering problem or don't matter on an
> Arm Juno board (whatever that is).  Can someone explain?

Hi Alex,

Thanks for replying!

Laurent was positing that doing the bus_set_iommu() call in the probe
function will break setups 

> If there's a
> desire for a stable tag for this, it seems like we need to know
> explicitly the range where it's safe to apply.  Also, the patch needs
> to be updated and re-evaluated in the presence of:
> 
> cda52fcd999f iommu/ipmmu-vmsa: Make use of IOMMU_OF_DECLARE()
> 
> Thanks,
> Alex
> 
> > > > 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>");
> > > >   
> > >   
> > 
> 

-- 
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