Re: [PATCH v2 1/2] iommu: add support for drivers that manage iommu explicitly

From: Robin Murphy <robin.murphy@arm.com>
To: Rob Clark <robdclark@gmail.com>, Joerg Roedel <joro@8bytes.org>
Cc: Rob Clark <robdclark@chromium.org>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	open list <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	iommu@lists.linux-foundation.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Joe Perches <joe@perches.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Will Deacon <will@kernel.org>,
	Bartosz Golaszewski <brgl@bgdev.pl>
Subject: Re: [PATCH v2 1/2] iommu: add support for drivers that manage iommu explicitly
Date: Tue, 10 Sep 2019 17:51:57 +0100	[thread overview]
Message-ID: <4b5b59bb-39a4-0757-e2bb-0961cfc7e4c1@arm.com> (raw)
In-Reply-To: <CAF6AEGsFmuO5M_RWm-RjDT_F_1Z=MLYmNqRXqFNDR7aUoPaMdg@mail.gmail.com>

On 10/09/2019 16:34, Rob Clark wrote:
> On Tue, Sep 10, 2019 at 1:14 AM Joerg Roedel <joro@8bytes.org> wrote:
>>
>> On Fri, Sep 06, 2019 at 02:44:01PM -0700, Rob Clark wrote:
>>> @@ -674,7 +674,7 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
>>>
>>>        mutex_lock(&group->mutex);
>>>        list_add_tail(&device->list, &group->devices);
>>> -     if (group->domain)
>>> +     if (group->domain && !(dev->driver && dev->driver->driver_manages_iommu))
>>
>> Hmm, this code usually runs at enumeration time when no driver is
>> attached to the device. Actually it would be pretty dangerous when this
>> code runs while a driver is attached to the device. How does that change
>> make things work for you?
>>
> 
> I was seeing this get called via the path driver_probe_device() ->
> platform_dma_configure() -> of_dma_configure() -> of_iommu_configure()
> -> iommu_probe_device() -> ...
> 
> The only cases I was seeing where dev->driver is NULL where a few
> places that drivers call of_dma_configure() on their own sub-devices.
> But maybe there are some other paths that I did not notice?

For the of_iommu flow, it very much depends on your DT layout and driver 
probe order as to whether you catch the "proper" call from 
iommu_bus_notifier()/iommu_bus_init() or the late "replay" from 
of_iommu_configure(). I wouldn't make any assumptions of consistency.

Robin.
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