linux-kernel - Re: [PATCH] iommu/of: Only do IOMMU lookup for available ones

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Message-ID: <20180118144118.GA12394@arm.com>
Date:   Thu, 18 Jan 2018 14:41:18 +0000
From:   Will Deacon <will.deacon@....com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Jeffy Chen <jeffy.chen@...k-chips.com>,
        linux-kernel@...r.kernel.org, jcliang@...omium.org,
        tfiga@...omium.org, iommu@...ts.linux-foundation.org,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH] iommu/of: Only do IOMMU lookup for available ones

On Wed, Jan 17, 2018 at 02:28:08PM +0100, Joerg Roedel wrote:
> On Wed, Jan 03, 2018 at 02:09:20PM +0800, Jeffy Chen wrote:
> > The for_each_matching_node_and_match() would return every matching
> > nodes including unavailable ones.
> > 
> > It's pointless to init unavailable IOMMUs, so add a sanity check to
> > avoid that.
> > 
> > Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> > ---
> > 
> >  drivers/iommu/of_iommu.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> > index 50947ebb6d17..6f7456caa30d 100644
> > --- a/drivers/iommu/of_iommu.c
> > +++ b/drivers/iommu/of_iommu.c
> > @@ -240,6 +240,9 @@ static int __init of_iommu_init(void)
> >  	for_each_matching_node_and_match(np, matches, &match) {
> >  		const of_iommu_init_fn init_fn = match->data;
> >  
> > +		if (!of_device_is_available(np))
> > +			continue;
> > +
> 
> Makes sense to me, but I'd like to have an OK from Robin or Will (added
> to Cc) before applying this.

I don't think this patch makes a lot of sense in isolation: the SMMU drivers
themselves will likely still probe, and it's unclear what we should about
DMA when an IOMMU is not deemed to be available. See:

https://patchwork.kernel.org/patch/9681211/

Jeffy -- are you solving a real issue here, or is this just an attempt at
some cleanup?

Will