[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[Robin Murphy]

We now delay installing our per-bus iommu_ops until we know an SMMU has
successfully probed, as they don't serve much purpose beforehand, and
doing so also avoids fights between multiple IOMMU drivers in a single
kernel. However, the upshot of passing the return value of bus_set_iommu()
back from our probe function is that if there happens to be more than
one SMMUv3 device in a system, the second and subsequent probes will
wind up returning -EBUSY to the driver core and getting torn down again.

There are essentially 3 cases in which bus_set_iommu() returns nonzero:
1. The bus already has iommu_ops installed
2. One of the add_device callbacks from the initial notifier failed
3. Allocating or installing the notifier itself failed

The first two are down to devices other than the SMMU in question, so
shouldn't abort an otherwise-successful SMMU probe, whilst the third is
indicative of the kind of catastrophic system failure which isn't going
to get much further anyway. Consequently, there is little harm in
ignoring the return value either way.

CC: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/arm-smmu-v3.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 15c01c3cd540..74fbef384deb 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -2637,16 +2637,13 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
 	of_iommu_set_ops(dev->of_node, &arm_smmu_ops);
 #ifdef CONFIG_PCI
 	pci_request_acs();
-	ret = bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
-	if (ret)
-		return ret;
+	bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
 #endif
 #ifdef CONFIG_ARM_AMBA
-	ret = bus_set_iommu(&amba_bustype, &arm_smmu_ops);
-	if (ret)
-		return ret;
+	bus_set_iommu(&amba_bustype, &arm_smmu_ops);
 #endif
-	return bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
+	bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
+	return 0;
 }
 
 static int arm_smmu_device_remove(struct platform_device *pdev)
-- 
1.9.1

[PATCH 2/2] iommu/arm-smmu: Work around ARM DMA configuration

[Robin Murphy]

The 32-bit ARM DMA configuration code predates the IOMMU core's default
domain functionality, and instead relies on allocating its own domains
and attaching any devices using the generic IOMMU binding to them.
Unfortunately, it does this relatively early on in the creation of the
device, before we've seen our add_device callback, which leads us to
attempt to operate on a half-configured master.

To avoid a crash, check for this situation on attach, but refuse to
play, as there's nothing we can do. This at least allows VFIO to keep
working for people who update their 32-bit DTs to the generic binding,
albeit with a few (innocuous) warnings from the DMA layer on boot.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/arm-smmu.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index c841eb7a1a74..3af7f8f62d0a 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1228,6 +1228,16 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 		return -ENXIO;
 	}
 
+	/*
+	 * FIXME: The arch/arm DMA API code tries to attach devices to its own
+	 * domains between of_xlate() and add_device() - we have no way to cope
+	 * with that, so until ARM gets converted to rely on groups and default
+	 * domains, just say no (but more politely than by dereferencing NULL).
+	 * This should be at least a WARN_ON once that's sorted.
+	 */
+	if (!fwspec->iommu_priv)
+		return -ENODEV;
+
 	smmu = fwspec_smmu(fwspec);
 	/* Ensure that the domain is finalised */
 	ret = arm_smmu_init_domain_context(domain, smmu);
-- 
1.9.1

[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[Lorenzo Pieralisi]

On Mon, Oct 17, 2016 at 12:06:20PM +0100, Robin Murphy wrote:
> We now delay installing our per-bus iommu_ops until we know an SMMU has
> successfully probed, as they don't serve much purpose beforehand, and
> doing so also avoids fights between multiple IOMMU drivers in a single
> kernel. However, the upshot of passing the return value of bus_set_iommu()
> back from our probe function is that if there happens to be more than
> one SMMUv3 device in a system, the second and subsequent probes will
> wind up returning -EBUSY to the driver core and getting torn down again.
> 
> There are essentially 3 cases in which bus_set_iommu() returns nonzero:
> 1. The bus already has iommu_ops installed
> 2. One of the add_device callbacks from the initial notifier failed
> 3. Allocating or installing the notifier itself failed
> 
> The first two are down to devices other than the SMMU in question, so
> shouldn't abort an otherwise-successful SMMU probe, whilst the third is
> indicative of the kind of catastrophic system failure which isn't going
> to get much further anyway. Consequently, there is little harm in
> ignoring the return value either way.
> 
> CC: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/iommu/arm-smmu-v3.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index 15c01c3cd540..74fbef384deb 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -2637,16 +2637,13 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
>  	of_iommu_set_ops(dev->of_node, &arm_smmu_ops);
>  #ifdef CONFIG_PCI
>  	pci_request_acs();
> -	ret = bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
> -	if (ret)
> -		return ret;
> +	bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
>  #endif
>  #ifdef CONFIG_ARM_AMBA
> -	ret = bus_set_iommu(&amba_bustype, &arm_smmu_ops);
> -	if (ret)
> -		return ret;
> +	bus_set_iommu(&amba_bustype, &arm_smmu_ops);
>  #endif
> -	return bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
> +	bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
> +	return 0;

Nit: I do not see why you would not take the same approach as
the ARM SMMUv1/v2, namely checking if ops are already set and
skip the call if that's the case.

Anyway:

Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

>  }
>  
>  static int arm_smmu_device_remove(struct platform_device *pdev)
> -- 
> 1.9.1
> 

[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[Sricharan]

Hi,

>-----Original Message-----
>From: linux-arm-kernel [mailto:linux-arm-kernel-bounces at lists.infradead.org] On Behalf Of Robin Murphy
>Sent: Monday, October 17, 2016 4:36 PM
>To: will.deacon at arm.com; joro at 8bytes.org
>Cc: iommu at lists.linux-foundation.org; Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>; linux-arm-kernel at lists.infradead.org
>Subject: [PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s
>
>We now delay installing our per-bus iommu_ops until we know an SMMU has
>successfully probed, as they don't serve much purpose beforehand, and
>doing so also avoids fights between multiple IOMMU drivers in a single
>kernel. However, the upshot of passing the return value of bus_set_iommu()
>back from our probe function is that if there happens to be more than
>one SMMUv3 device in a system, the second and subsequent probes will
>wind up returning -EBUSY to the driver core and getting torn down again.
>
>There are essentially 3 cases in which bus_set_iommu() returns nonzero:
>1. The bus already has iommu_ops installed
>2. One of the add_device callbacks from the initial notifier failed
>3. Allocating or installing the notifier itself failed
>
>The first two are down to devices other than the SMMU in question, so
>shouldn't abort an otherwise-successful SMMU probe, whilst the third is
>indicative of the kind of catastrophic system failure which isn't going
>to get much further anyway. Consequently, there is little harm in
>ignoring the return value either way.
>
>CC: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
>Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>---
> drivers/iommu/arm-smmu-v3.c | 11 ++++-------
> 1 file changed, 4 insertions(+), 7 deletions(-)
>
>diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>index 15c01c3cd540..74fbef384deb 100644
>--- a/drivers/iommu/arm-smmu-v3.c
>+++ b/drivers/iommu/arm-smmu-v3.c
>@@ -2637,16 +2637,13 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
> 	of_iommu_set_ops(dev->of_node, &arm_smmu_ops);
> #ifdef CONFIG_PCI
> 	pci_request_acs();
>-	ret = bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
>-	if (ret)
>-		return ret;
>+	bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
> #endif
> #ifdef CONFIG_ARM_AMBA
>-	ret = bus_set_iommu(&amba_bustype, &arm_smmu_ops);
>-	if (ret)
>-		return ret;
>+	bus_set_iommu(&amba_bustype, &arm_smmu_ops);
> #endif
>-	return bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
>+	bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
>+	return 0;
    reviewed-by: sricharan at codeaurora.org

Regards,
 Sricharan
  

[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[Robin Murphy]

Hi Lorenzo,

On 17/10/16 14:21, Lorenzo Pieralisi wrote:
> On Mon, Oct 17, 2016 at 12:06:20PM +0100, Robin Murphy wrote:
>> We now delay installing our per-bus iommu_ops until we know an SMMU has
>> successfully probed, as they don't serve much purpose beforehand, and
>> doing so also avoids fights between multiple IOMMU drivers in a single
>> kernel. However, the upshot of passing the return value of bus_set_iommu()
>> back from our probe function is that if there happens to be more than
>> one SMMUv3 device in a system, the second and subsequent probes will
>> wind up returning -EBUSY to the driver core and getting torn down again.
>>
>> There are essentially 3 cases in which bus_set_iommu() returns nonzero:
>> 1. The bus already has iommu_ops installed
>> 2. One of the add_device callbacks from the initial notifier failed
>> 3. Allocating or installing the notifier itself failed
>>
>> The first two are down to devices other than the SMMU in question, so
>> shouldn't abort an otherwise-successful SMMU probe, whilst the third is
>> indicative of the kind of catastrophic system failure which isn't going
>> to get much further anyway. Consequently, there is little harm in
>> ignoring the return value either way.
>>
>> CC: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>  drivers/iommu/arm-smmu-v3.c | 11 ++++-------
>>  1 file changed, 4 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>> index 15c01c3cd540..74fbef384deb 100644
>> --- a/drivers/iommu/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm-smmu-v3.c
>> @@ -2637,16 +2637,13 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
>>  	of_iommu_set_ops(dev->of_node, &arm_smmu_ops);
>>  #ifdef CONFIG_PCI
>>  	pci_request_acs();
>> -	ret = bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
>> -	if (ret)
>> -		return ret;
>> +	bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
>>  #endif
>>  #ifdef CONFIG_ARM_AMBA
>> -	ret = bus_set_iommu(&amba_bustype, &arm_smmu_ops);
>> -	if (ret)
>> -		return ret;
>> +	bus_set_iommu(&amba_bustype, &arm_smmu_ops);
>>  #endif
>> -	return bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
>> +	bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
>> +	return 0;
> 
> Nit: I do not see why you would not take the same approach as
> the ARM SMMUv1/v2, namely checking if ops are already set and
> skip the call if that's the case.

Well, I'd say it really goes the other way around - since the very first
thing bus_set_iommu() does is check if ops are present, and return if
so, and the v2 driver already doesn't care about that return value,
there's not really any need for it to duplicate the check either. I
didn't change it at the time to avoid cluttering the gigantic rework any
further, but I could spin a cleanup patch if you like.

> Anyway:
> 
> Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

Thanks!

Robin.

[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[Lorenzo Pieralisi]

On Mon, Oct 17, 2016 at 03:19:46PM +0100, Robin Murphy wrote:
> Hi Lorenzo,
> 
> On 17/10/16 14:21, Lorenzo Pieralisi wrote:
> > On Mon, Oct 17, 2016 at 12:06:20PM +0100, Robin Murphy wrote:
> >> We now delay installing our per-bus iommu_ops until we know an SMMU has
> >> successfully probed, as they don't serve much purpose beforehand, and
> >> doing so also avoids fights between multiple IOMMU drivers in a single
> >> kernel. However, the upshot of passing the return value of bus_set_iommu()
> >> back from our probe function is that if there happens to be more than
> >> one SMMUv3 device in a system, the second and subsequent probes will
> >> wind up returning -EBUSY to the driver core and getting torn down again.
> >>
> >> There are essentially 3 cases in which bus_set_iommu() returns nonzero:
> >> 1. The bus already has iommu_ops installed
> >> 2. One of the add_device callbacks from the initial notifier failed
> >> 3. Allocating or installing the notifier itself failed
> >>
> >> The first two are down to devices other than the SMMU in question, so
> >> shouldn't abort an otherwise-successful SMMU probe, whilst the third is
> >> indicative of the kind of catastrophic system failure which isn't going
> >> to get much further anyway. Consequently, there is little harm in
> >> ignoring the return value either way.
> >>
> >> CC: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> >> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> >> ---
> >>  drivers/iommu/arm-smmu-v3.c | 11 ++++-------
> >>  1 file changed, 4 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> >> index 15c01c3cd540..74fbef384deb 100644
> >> --- a/drivers/iommu/arm-smmu-v3.c
> >> +++ b/drivers/iommu/arm-smmu-v3.c
> >> @@ -2637,16 +2637,13 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
> >>  	of_iommu_set_ops(dev->of_node, &arm_smmu_ops);
> >>  #ifdef CONFIG_PCI
> >>  	pci_request_acs();
> >> -	ret = bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
> >> -	if (ret)
> >> -		return ret;
> >> +	bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
> >>  #endif
> >>  #ifdef CONFIG_ARM_AMBA
> >> -	ret = bus_set_iommu(&amba_bustype, &arm_smmu_ops);
> >> -	if (ret)
> >> -		return ret;
> >> +	bus_set_iommu(&amba_bustype, &arm_smmu_ops);
> >>  #endif
> >> -	return bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
> >> +	bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
> >> +	return 0;
> > 
> > Nit: I do not see why you would not take the same approach as
> > the ARM SMMUv1/v2, namely checking if ops are already set and
> > skip the call if that's the case.
> 
> Well, I'd say it really goes the other way around - since the very first
> thing bus_set_iommu() does is check if ops are present, and return if
> so, and the v2 driver already doesn't care about that return value,
> there's not really any need for it to duplicate the check either. I
> didn't change it at the time to avoid cluttering the gigantic rework any
> further, but I could spin a cleanup patch if you like.

No worries, it was to understand if there was a reason to keep
the code different and after another look I agree with what
you are saying (by checking if ops are present you could eg
avoid calling pci_request_acs() every probe but that's a detail).

Thanks for fixing it !
Lorenzo

> > Anyway:
> > 
> > Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> 
> Thanks!
> 
> Robin.
> 

[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[Will Deacon]

On Mon, Oct 17, 2016 at 12:06:20PM +0100, Robin Murphy wrote:
> We now delay installing our per-bus iommu_ops until we know an SMMU has
> successfully probed, as they don't serve much purpose beforehand, and
> doing so also avoids fights between multiple IOMMU drivers in a single
> kernel. However, the upshot of passing the return value of bus_set_iommu()
> back from our probe function is that if there happens to be more than
> one SMMUv3 device in a system, the second and subsequent probes will
> wind up returning -EBUSY to the driver core and getting torn down again.
> 
> There are essentially 3 cases in which bus_set_iommu() returns nonzero:
> 1. The bus already has iommu_ops installed
> 2. One of the add_device callbacks from the initial notifier failed
> 3. Allocating or installing the notifier itself failed
> 
> The first two are down to devices other than the SMMU in question, so
> shouldn't abort an otherwise-successful SMMU probe, whilst the third is
> indicative of the kind of catastrophic system failure which isn't going
> to get much further anyway. Consequently, there is little harm in
> ignoring the return value either way.
> 
> CC: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/iommu/arm-smmu-v3.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index 15c01c3cd540..74fbef384deb 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -2637,16 +2637,13 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
>  	of_iommu_set_ops(dev->of_node, &arm_smmu_ops);
>  #ifdef CONFIG_PCI
>  	pci_request_acs();
> -	ret = bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
> -	if (ret)
> -		return ret;
> +	bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
>  #endif
>  #ifdef CONFIG_ARM_AMBA
> -	ret = bus_set_iommu(&amba_bustype, &arm_smmu_ops);
> -	if (ret)
> -		return ret;
> +	bus_set_iommu(&amba_bustype, &arm_smmu_ops);
>  #endif
> -	return bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
> +	bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
> +	return 0;

In which case, we should probably add an iommu_present check, like we
have for the v2 driver.

Will

[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[Robin Murphy]

On 19/10/16 13:49, Will Deacon wrote:
> On Mon, Oct 17, 2016 at 12:06:20PM +0100, Robin Murphy wrote:
>> We now delay installing our per-bus iommu_ops until we know an SMMU has
>> successfully probed, as they don't serve much purpose beforehand, and
>> doing so also avoids fights between multiple IOMMU drivers in a single
>> kernel. However, the upshot of passing the return value of bus_set_iommu()
>> back from our probe function is that if there happens to be more than
>> one SMMUv3 device in a system, the second and subsequent probes will
>> wind up returning -EBUSY to the driver core and getting torn down again.
>>
>> There are essentially 3 cases in which bus_set_iommu() returns nonzero:
>> 1. The bus already has iommu_ops installed
>> 2. One of the add_device callbacks from the initial notifier failed
>> 3. Allocating or installing the notifier itself failed
>>
>> The first two are down to devices other than the SMMU in question, so
>> shouldn't abort an otherwise-successful SMMU probe, whilst the third is
>> indicative of the kind of catastrophic system failure which isn't going
>> to get much further anyway. Consequently, there is little harm in
>> ignoring the return value either way.
>>
>> CC: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>  drivers/iommu/arm-smmu-v3.c | 11 ++++-------
>>  1 file changed, 4 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>> index 15c01c3cd540..74fbef384deb 100644
>> --- a/drivers/iommu/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm-smmu-v3.c
>> @@ -2637,16 +2637,13 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
>>  	of_iommu_set_ops(dev->of_node, &arm_smmu_ops);
>>  #ifdef CONFIG_PCI
>>  	pci_request_acs();
>> -	ret = bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
>> -	if (ret)
>> -		return ret;
>> +	bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
>>  #endif
>>  #ifdef CONFIG_ARM_AMBA
>> -	ret = bus_set_iommu(&amba_bustype, &arm_smmu_ops);
>> -	if (ret)
>> -		return ret;
>> +	bus_set_iommu(&amba_bustype, &arm_smmu_ops);
>>  #endif
>> -	return bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
>> +	bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
>> +	return 0;
> 
> In which case, we should probably add an iommu_present check, like we
> have for the v2 driver.

As touched upon in the commit message, the first thing bus_set_iommu()
does is perform that same check and return immediately if any ops are
already set. Do you really want redundant checks added, or shall I spin
that cleanup patch removing them from v2 that I proposed to Lorenzo?

Robin.

> 
> Will
> 

[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[Hanjun Guo]

On 2016/10/17 19:06, Robin Murphy wrote:
> We now delay installing our per-bus iommu_ops until we know an SMMU has
> successfully probed, as they don't serve much purpose beforehand, and
> doing so also avoids fights between multiple IOMMU drivers in a single
> kernel. However, the upshot of passing the return value of bus_set_iommu()
> back from our probe function is that if there happens to be more than
> one SMMUv3 device in a system, the second and subsequent probes will
> wind up returning -EBUSY to the driver core and getting torn down again.
>
> There are essentially 3 cases in which bus_set_iommu() returns nonzero:
> 1. The bus already has iommu_ops installed
> 2. One of the add_device callbacks from the initial notifier failed
> 3. Allocating or installing the notifier itself failed
>
> The first two are down to devices other than the SMMU in question, so
> shouldn't abort an otherwise-successful SMMU probe, whilst the third is
> indicative of the kind of catastrophic system failure which isn't going
> to get much further anyway. Consequently, there is little harm in
> ignoring the return value either way.
>
> CC: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

Tested-by: Hanjun Guo <hanjun.guo@linaro.org>

Thanks
Hanjun

[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[Will Deacon]

On Fri, Oct 21, 2016 at 05:20:43PM +0100, Robin Murphy wrote:
> On 19/10/16 13:49, Will Deacon wrote:
> > On Mon, Oct 17, 2016 at 12:06:20PM +0100, Robin Murphy wrote:
> >> We now delay installing our per-bus iommu_ops until we know an SMMU has
> >> successfully probed, as they don't serve much purpose beforehand, and
> >> doing so also avoids fights between multiple IOMMU drivers in a single
> >> kernel. However, the upshot of passing the return value of bus_set_iommu()
> >> back from our probe function is that if there happens to be more than
> >> one SMMUv3 device in a system, the second and subsequent probes will
> >> wind up returning -EBUSY to the driver core and getting torn down again.
> >>
> >> There are essentially 3 cases in which bus_set_iommu() returns nonzero:
> >> 1. The bus already has iommu_ops installed
> >> 2. One of the add_device callbacks from the initial notifier failed
> >> 3. Allocating or installing the notifier itself failed
> >>
> >> The first two are down to devices other than the SMMU in question, so
> >> shouldn't abort an otherwise-successful SMMU probe, whilst the third is
> >> indicative of the kind of catastrophic system failure which isn't going
> >> to get much further anyway. Consequently, there is little harm in
> >> ignoring the return value either way.
> >>
> >> CC: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> >> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> >> ---
> >>  drivers/iommu/arm-smmu-v3.c | 11 ++++-------
> >>  1 file changed, 4 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> >> index 15c01c3cd540..74fbef384deb 100644
> >> --- a/drivers/iommu/arm-smmu-v3.c
> >> +++ b/drivers/iommu/arm-smmu-v3.c
> >> @@ -2637,16 +2637,13 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
> >>  	of_iommu_set_ops(dev->of_node, &arm_smmu_ops);
> >>  #ifdef CONFIG_PCI
> >>  	pci_request_acs();
> >> -	ret = bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
> >> -	if (ret)
> >> -		return ret;
> >> +	bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
> >>  #endif
> >>  #ifdef CONFIG_ARM_AMBA
> >> -	ret = bus_set_iommu(&amba_bustype, &arm_smmu_ops);
> >> -	if (ret)
> >> -		return ret;
> >> +	bus_set_iommu(&amba_bustype, &arm_smmu_ops);
> >>  #endif
> >> -	return bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
> >> +	bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
> >> +	return 0;
> > 
> > In which case, we should probably add an iommu_present check, like we
> > have for the v2 driver.
> 
> As touched upon in the commit message, the first thing bus_set_iommu()
> does is perform that same check and return immediately if any ops are
> already set. Do you really want redundant checks added, or shall I spin
> that cleanup patch removing them from v2 that I proposed to Lorenzo?

A cleanup patch sounds good, to keep the two drivers consistent.

Will