linux-kernel - Re: [PATCHv5 4/9] iommu/tegra: smmu: register device to iommu dynamically

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Message-ID: <20131121153845.e37c01b2f384883e3611790a@nvidia.com>
Date:	Thu, 21 Nov 2013 15:38:45 +0200
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	"will.deacon@....com" <will.deacon@....com>,
	Grant Likely <grant.likely@...aro.org>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Stephen Warren <swarren@...dia.com>,
	"thierry.reding@...il.com" <thierry.reding@...il.com>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv5 4/9] iommu/tegra: smmu: register device to iommu
 dynamically

On Thu, 21 Nov 2013 14:23:22 +0100
Grant Likely <grant.likely@...aro.org> wrote:

> > > +static int smmu_iommu_add_device(struct device *dev)
> > > +{
> > > +	int err = -EPROBE_DEFER;
> > > +	u32 swgroups = dev->platform_data;
> > > +	struct dma_iommu_mapping *map = NULL;
> > > +
> > > +	if (test_bit(TEGRA_SWGROUP_PPCS, swgroups))
> > > +		map = smmu_handle->map[SYSTEM_PROTECTED];
> > > +	else
> > > +		map = smmu_handle->map[SYSTEM_DEFAULT];
> > > +
> > > +	if (map)
> > > +		err = arm_iommu_attach_device(dev, map);
> > > +	else
> > > +		return -EPROBE_DEFER;
> > 
> > Given that patch 2 exists, if this test fails, then surely the
> > appropriate error code is some fatal error, not -EPROBE_DEFER; any
> > deferrals should have happened long before this point.
> 
> Will need to be revisited. Patching into the core really_probe() like
> patch #2 does is a really bad approach which would mean that returning
> EPROBE_DEFER is appropriate here.

I'm going to send PATCHv6, where it's a little bit easier to discuss
further since some code are cleaned up with feedback.

We once discussed to make use of bus_notifier instead of embedding a
hook in really_probe(). This would require some change where
bus_notifer return code needs to be used to postpone device
population.
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