[PATCH v2 5/5] iommu: Allow default domain type to be set on the kernel command line
Sricharan R
sricharan at codeaurora.org
Thu Mar 23 03:22:06 PDT 2017
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
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