linux-kernel - Re: [PATCH v6 05/07] iommu/ipmmu-vmsa: Add new IOMMU_DOMAIN

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Date:   Fri, 11 Nov 2016 03:50:44 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Magnus Damm <magnus.damm@...il.com>,
        iommu@...ts.linux-foundation.org,
        laurent.pinchart+renesas@...asonboard.com, geert+renesas@...der.be,
        joro@...tes.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, horms+renesas@...ge.net.au,
        m.szyprowski@...sung.com
Subject: Re: [PATCH v6 05/07] iommu/ipmmu-vmsa: Add new IOMMU_DOMAIN_DMA ops

Hi Robin,

On Friday 21 Oct 2016 18:52:53 Robin Murphy wrote:
> On 20/10/16 00:36, Magnus Damm wrote:
> > From: Magnus Damm <damm+renesas@...nsource.se>
> > 
> > Introduce an alternative set of iommu_ops suitable for 64-bit ARM
> > as well as 32-bit ARM when CONFIG_IOMMU_DMA=y. Also adjust the
> > Kconfig to depend on ARM or IOMMU_DMA.
> > 
> > Signed-off-by: Magnus Damm <damm+renesas@...nsource.se>
> > ---
> > 
> >  Changes since V5:
> >  - Made domain allocation/free code more consistent - thanks Joerg!
> >  
> >  Changes since V4:
> >  - Added Kconfig hunk to depend on ARM or IOMMU_DMA
> >  
> >  Changes since V3:
> >  - Removed group parameter from ipmmu_init_platform_device()
> >  
> >  Changes since V2:
> >  
> >  - Included this new patch from the following series:
> >    [PATCH 00/04] iommu/ipmmu-vmsa: IPMMU CONFIG_IOMMU_DMA update
> >  
> >  - Use only a single iommu_ops structure with #ifdef CONFIG_IOMMU_DMA
> >  - Folded in #ifdefs to handle CONFIG_ARM and CONFIG_IOMMU_DMA
> >  - of_xlate() is now used without #ifdefs
> >  - Made sure code compiles on both 32-bit and 64-bit ARM.
> >  
> >  drivers/iommu/Kconfig      |    1
> >  drivers/iommu/ipmmu-vmsa.c |  122 ++++++++++++++++++++++++++++++++++++---
> >  2 files changed, 115 insertions(+), 8 deletions(-)

[snip]

> > --- 0006/drivers/iommu/ipmmu-vmsa.c
> > +++ work/drivers/iommu/ipmmu-vmsa.c	2016-10-20 08:16:48.440607110 +0900

[snip]

> > -static struct iommu_domain *ipmmu_domain_alloc(unsigned type)
> > -{
> > -	if (type != IOMMU_DOMAIN_UNMANAGED)
> > -		return NULL;
> 
> I *think* that if we did the initial check thus:
> 
> 	if (type != IOMMU_DOMAIN_UNMANAGED ||
> 	    (IS_ENABLED(CONFIG_IOMMU_DMA) && type != IOMMU_DOMAIN_DMA))
> 		return NULL;

I assume you meant

 	if (type != IOMMU_DOMAIN_UNMANAGED &&
 	    (!IS_ENABLED(CONFIG_IOMMU_DMA) || type != IOMMU_DOMAIN_DMA))
 		return NULL;

But how about just

 	if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA))
 		return NULL;

as type will never be set to IOMMU_DOMAIN_DMA on ARM32 ?

> it shouldn't be necessary to split the function at all - we then just
> wrap the {get,put}_cookie() bits in "if (type ==  IOMMU_DOMAIN_DMA)" and
> in the 32-bit ARM case they just don't run as that can never be true.
> 
> > -
> > -	return __ipmmu_domain_alloc(type);
> > -}
> > -

-- 
Regards,

Laurent Pinchart