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

[Alex Williamson]

On Tue, 21 Nov 2017 12:08:01 +0000
Liviu Dudau <Liviu.Dudau@xxxxxxx> wrote:

> 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@xxxxxxx> 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 

Yes, I understood that.  Replying that it was on an Arm64 Juno board
did not in any way clarify to me how that concern is addressed.  Thanks,

Alex

> > 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@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 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@xxxxxxxxxxxxxxxx>");
> > > > >     
> > > >     
> > >   
> >   
>