[PATCH v2 5/5] iommu: Allow default domain type to be set on the kernel command line

[Sricharan R]

Hi,

On 3/21/2017 11:47 PM, Will Deacon wrote:
> On Tue, Mar 21, 2017 at 05:46:29PM +0000, Robin Murphy wrote:
>> On 21/03/17 17:21, Will Deacon wrote:
>>> On Tue, Mar 21, 2017 at 04:45:27PM +0100, Joerg Roedel wrote:
>>>> On Fri, Mar 10, 2017 at 08:49:36PM +0000, Will Deacon wrote:
>>>>> @@ -1014,8 +1027,8 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
>>>>>  	 * IOMMU driver.
>>>>>  	 */
>>>>>  	if (!group->default_domain) {
>>>>> -		group->default_domain = __iommu_domain_alloc(dev->bus,
>>>>> -							     IOMMU_DOMAIN_DMA);
>>>>> +		group->default_domain =
>>>>> +			__iommu_domain_alloc(dev->bus, iommu_def_domain_type);
>>>>
>>>> It would be good to have a fall-back here if we are talking to an IOMMU
>>>> driver that uses default domains, but does not support identity-mapped
>>>> domains (yet). Exynos and Rockchip IOMMU drivers seem to fall into this
>>>> category. A dev_warn() also makes sense in case allocating a identity
>>>> domain fails.
>>>
>>> Sure, something like the diff below?
>>>
>>> Will
>>>
>>> --->8
>>>
>>>
>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>>> index 42a842e3f95f..f787626a745d 100644
>>> --- a/drivers/iommu/iommu.c
>>> +++ b/drivers/iommu/iommu.c
>>> @@ -1027,10 +1027,19 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
>>>  	 * IOMMU driver.
>>>  	 */
>>>  	if (!group->default_domain) {
>>> -		group->default_domain =
>>> -			__iommu_domain_alloc(dev->bus, iommu_def_domain_type);
>>> +		struct iommu_domain *dom;
>>> +
>>> +		dom = __iommu_domain_alloc(dev->bus, iommu_def_domain_type);
>>> +		if (!dom) {
>>> +			dev_warn(dev,
>>> +				 "failed to allocate default IOMMU domain of type %u; falling back to IOMMU_DOMAIN_DMA",
>>> +				 iommu_def_domain_type);
>>
>> Conversely, that's going to be noisy if iommu_def_domain_type was
>> IOMMU_DOMAIN_DMA to begin with. I think it makes sense to warn if the
>> user asked for a specific default domain type on the command line and
>> that didn't work, but maybe not to bother otherwise. Plus, if they asked
>> for passthrough, then not allocating a default domain at all is probably
>> closer to the desired result than installing a DMA ops domain would be.
>
> You're right -- I'll hack this about to check if the default type isn't
> DOMAIN_DMA before warning about the allocation failure.

if some master devices want 'IDENTITY_DOMAIN' as default (because  those 
devices do not want any iommu resources to be used/dma_ops to be set) 
and some 'DMA_DOMAIN' as default, then should the default be 
'DMA_DOMAIN' and then masters needing IDENTITY_DOMAIN explicitly do an
detach_dev later. This [1] was adding the support for detach_dev
of the default DMA_DOMAINs.

[1] https://patchwork.codeaurora.org/patch/164933/

Regards,
  Sricharan