linux-kernel - Re: [PATCH 1/7] iommu/omap: Do bus_set

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Message-ID: <52D6C185.2090303@epfl.ch>
Date:	Wed, 15 Jan 2014 18:12:37 +0100
From:	Florian Vaussard <florian.vaussard@...l.ch>
To:	"Anna, Suman" <s-anna@...com>, Joerg Roedel <joro@...tes.org>,
	Tony Lindgren <tony@...mide.com>,
	Benoît Cousson <bcousson@...libre.com>
CC:	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Rob Landley <rob@...dley.net>,
	Grant Likely <grant.likely@...aro.org>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/7] iommu/omap: Do bus_set_iommu() only if probe() succeeds

Hi Suman,

So back to this...

On 12/24/2013 12:35 AM, Anna, Suman wrote:
> Hi Florian,
> 

[...]

>>
>> If omap_iommu_probe() fails, the init will have called bus_set_iommu()
>> anyways. Thus, when a driver request the iommu by calling
>> iommu_domain_alloc(), it will succeed (but iommu_attach_device() will
>> fail if I remember).
> 
> Yeah, thats the behavior I expected anyway.
> 
>> Leaving a driver with a dangling reference to
>> a phantom iommu is not good IMHO. It will lead to strange behaviours
>> one day or another.
>>
>> As for the multiple iommu case, as I do not think it is currently
>> possible, as bus_type (in this case &platform_bus_type) has only
>> one struct iommu_ops. bus_set_iommu() will return EBUSY on the
>> second call. Am I missing something?
> 
> What I meant was the problem you cited will still exist, say if ISP MMU
> probe failed, but the IVA MMU probe succeeded. The bus_set_iommu() can
> only be called once anyway, so moving it from init to probe would not
> help much.
> 

Ok I see your point. Similar IPs share the same ops, but with different
omap_iommu_arch_data, even if currently we only have one registered
IOMMU for OMAP3.

So I will drop this patch.

Regards,
Florian
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