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 ;)
Robin.
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
