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

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Date:   Tue, 10 Sep 2019 17:51:57 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Rob Clark <robdclark@...il.com>, Joerg Roedel <joro@...tes.org>
Cc:     "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Will Deacon <will@...nel.org>,
        Rob Clark <robdclark@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Sudeep Holla <sudeep.holla@....com>,
        Joe Perches <joe@...ches.com>, Arnd Bergmann <arnd@...db.de>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] iommu: add support for drivers that manage iommu
 explicitly

On 10/09/2019 16:34, Rob Clark wrote:
> On Tue, Sep 10, 2019 at 1:14 AM Joerg Roedel <joro@...tes.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.