Re: [PATCH] drivers/of_iommu: ignore SMMU DT nodes with status 'disabled'

Re: [PATCH] drivers/of_iommu: ignore SMMU DT nodes with status 'disabled'

[Will Deacon]

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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
>  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.

Will
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Re: [PATCH] drivers/of_iommu: ignore SMMU DT nodes with status 'disabled'

[Ard Biesheuvel]

On 28 April 2017 at 14:11, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> 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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
>> ---
>>  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.

Re: [PATCH] drivers/of_iommu: ignore SMMU DT nodes with status 'disabled'

[Will Deacon]

On Fri, Apr 28, 2017 at 02:14:49PM +0100, Ard Biesheuvel wrote:
> On 28 April 2017 at 14:11, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> 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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> >> ---
> >>  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.

Will
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Re: [PATCH] drivers/of_iommu: ignore SMMU DT nodes with status 'disabled'

[Ard Biesheuvel]

On 28 April 2017 at 14:17, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> 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-5wv7dgnIgG8@public.gmane.org> 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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
>> >> ---
>> >>  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
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Re: [PATCH] drivers/of_iommu: ignore SMMU DT nodes with status 'disabled'

[Robin Murphy]

On 28/04/17 14:22, Ard Biesheuvel wrote:
> On 28 April 2017 at 14:17, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> 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-5wv7dgnIgG8@public.gmane.org> 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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
>>>>> ---
>>>>>  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.

Re: [PATCH] drivers/of_iommu: ignore SMMU DT nodes with status 'disabled'

[Ard Biesheuvel]

> On 3 May 2017, at 11:32, Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org> wrote:
> 
>> On 28/04/17 14:22, Ard Biesheuvel wrote:
>>> On 28 April 2017 at 14:17, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> 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-5wv7dgnIgG8@public.gmane.org> 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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
>>>>>> ---
>>>>>> 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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