> On 3 May 2017, at 11:32, Robin Murphy <robin.murphy@xxxxxxx> wrote:
>
>> On 28/04/17 14:22, Ard Biesheuvel wrote:
>>> On 28 April 2017 at 14:17, Will Deacon <will.deacon@xxxxxxx> wrote:
>>>> On Fri, Apr 28, 2017 at 02:14:49PM +0100, Ard Biesheuvel wrote:
>>>>> On 28 April 2017 at 14:11, Will Deacon <will.deacon@xxxxxxx> wrote:
>>>>> Hi Ard,
>>>>>
>>>>> [+ devicetree@]
>>>>>
>>>>>> On Fri, Apr 14, 2017 at 01:43:15PM +0100, Ard Biesheuvel wrote:
>>>>>> DT nodes may have a status property, and if they do, such nodes should
>>>>>> only be considered present if the status property is set to 'okay'.
>>>>>>
>>>>>> Currently, we call the init function of IOMMUs described by the device
>>>>>> tree without taking this into account, which may result in the output
>>>>>> below on systems where some SMMUs may be legally disabled.
>>>>>>
>>>>>> Failed to initialise IOMMU /smb/smmu@e0200000
>>>>>> Failed to initialise IOMMU /smb/smmu@e0c00000
>>>>>> arm-smmu e0a00000.smmu: probing hardware configuration...
>>>>>> arm-smmu e0a00000.smmu: SMMUv1 with:
>>>>>> arm-smmu e0a00000.smmu: stage 2 translation
>>>>>> arm-smmu e0a00000.smmu: coherent table walk
>>>>>> arm-smmu e0a00000.smmu: stream matching with 32 register groups, mask 0x7fff
>>>>>> arm-smmu e0a00000.smmu: 8 context banks (8 stage-2 only)
>>>>>> arm-smmu e0a00000.smmu: Supported page sizes: 0x60211000
>>>>>> arm-smmu e0a00000.smmu: Stage-2: 40-bit IPA -> 40-bit PA
>>>>>> Failed to initialise IOMMU /smb/smmu@e0600000
>>>>>> Failed to initialise IOMMU /smb/smmu@e0800000
>>>>>>
>>>>>> Since this is not an error condition, only call the init function if
>>>>>> the device is enabled, which also inhibits the spurious error messages.
>>>>>>
>>>>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>>>>>> ---
>>>>>> drivers/iommu/of_iommu.c | 2 +-
>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
>>>>>> index 2683e9fc0dcf..2dd1206e6c0d 100644
>>>>>> --- a/drivers/iommu/of_iommu.c
>>>>>> +++ b/drivers/iommu/of_iommu.c
>>>>>> @@ -183,7 +183,7 @@ 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 (init_fn(np))
>>>>>> + if (of_device_is_available(np) && init_fn(np))
>>>>>> pr_err("Failed to initialise IOMMU %s\n",
>>>>>> of_node_full_name(np));
>>>>>> }
>>>>>
>>>>> Is there a definition of what status = "disabled" is supposed to mean for an
>>>>> IOMMU? For example, that could mean that the firmware has pre-programmed the
>>>>> SMMU with particular translations or memory attributes (a bit like the
>>>>> CCA=1, CPM=1, DACS=0 case in ACPI IORT), or even disabled DMA traffic
>>>>> altogether.
>>>>>
>>>>> So I think we'd need an update to the generic IOMMU binding text to say
>>>>> exactly what the semantics are supposed to be here.
>>>>>
>>>>
>>>> I agree that it might make sense to describe the behavior of the IOMMU
>>>> when it is left in the state we found it in. But that is not the same
>>>> as status=disabled.
>>>>
>>>> The DTS subtree contains loads and loads of boilerplate
>>>> configurations, where only some pieces are enabled in the final image
>>>> by setting status=okay. So a node that has status 'disabled' should be
>>>> treated as 'not present', not as 'present but can be ignored under
>>>> assumptions such and such'
>>>>
>>>> In other words, I think we are talking about two different issues here.
>>>
>>> I'm not so sure... if we have a master device that has an iommus= property
>>> pointing to an IOMMU with status="disabled", I really don't know whether we
>>> should:
>>>
>>> 1. Assume the master can do DMA with a 1:1 mapping of memory and no
>>> changes to memory attributes
>>>
>>> 2. Assume the master can do DMA with a 1:1 mapping of memory, but
>>> potentially with changes to the attributes
>>>
>>> 3. Assume the master can do DMA, but with some pre-existing translation
>>> (what?)
>>>
>>> 4. Assume the master can't do DMA
>>>
>>> and I also don't know whether the "dma-coherent" property remains valid.
>>>
>>
>> Ah yes. Good point.
>>
>> So indeed, there should be some IOMMU specific status property that
>> can convey all of the above, or 1. and 4. at the minimum
>
> FWIW, the underlying issue being addressed here should be going away now
> anyway, since the now-queued probe deferral series obviates the init_fn
> early-device-creation bodge. I've been deliberately ignoring it for some
> time for precisely that reason ;)
>
Ok. I have also updated the Seattle firmware to remove the smmu nodes and the associated iommus/iommu-map properties entirely when disabling SMMU support in the firmware, which should address Will's concern regarding unspecified behavior of a disabled SMMU.
IOW, this patch can be disregarded. Thanks.
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