On Thu, Jul 13, 2017 at 1:35 AM, Sricharan R <sricharan@xxxxxxxxxxxxxx> wrote:
> Hi Vivek,
>
> On 7/13/2017 10:43 AM, Vivek Gautam wrote:
>> Hi Stephen,
>>
>>
>> On 07/13/2017 04:24 AM, Stephen Boyd wrote:
>>> On 07/06, Vivek Gautam wrote:
>>>> @@ -1231,12 +1237,18 @@ static int arm_smmu_map(struct iommu_domain *domain, unsigned long iova,
>>>> static size_t arm_smmu_unmap(struct iommu_domain *domain, unsigned long iova,
>>>> size_t size)
>>>> {
>>>> - struct io_pgtable_ops *ops = to_smmu_domain(domain)->pgtbl_ops;
>>>> + struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>>>> + struct io_pgtable_ops *ops = smmu_domain->pgtbl_ops;
>>>> + size_t ret;
>>>> if (!ops)
>>>> return 0;
>>>> - return ops->unmap(ops, iova, size);
>>>> + pm_runtime_get_sync(smmu_domain->smmu->dev);
>>> Can these map/unmap ops be called from an atomic context? I seem
>>> to recall that being a problem before.
>>
>> That's something which was dropped in the following patch merged in master:
>> 523d7423e21b iommu/arm-smmu: Remove io-pgtable spinlock
>>
>> Looks like we don't need locks here anymore?
>
> Apart from the locking, wonder why a explicit pm_runtime is needed
> from unmap. Somehow looks like some path in the master using that
> should have enabled the pm ?
>
Yes, there are a bunch of scenarios where unmap can happen with
disabled master (but not in atomic context). On the gpu side we
opportunistically keep a buffer mapping until the buffer is freed
(which can happen after gpu is disabled). Likewise, v4l2 won't unmap
an exported dmabuf while some other driver holds a reference to it
(which can be dropped when the v4l2 device is suspended).
Since unmap triggers tbl flush which touches iommu regs, the iommu
driver *definitely* needs a pm_runtime_get_sync().
BR,
-R
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