Re: [PATCH V4 3/6] iommu/arm-smmu: Invoke pm_runtime during probe, add/remove device

[Vivek Gautam <vivek.gautam@codeaurora.org>]

Hi,


On Mon, Aug 7, 2017 at 5:59 PM, Rob Clark <robdclark@gmail.com> wrote:
> On Mon, Aug 7, 2017 at 4:27 AM, Vivek Gautam
> <vivek.gautam@codeaurora.org> wrote:
>> On Thu, Jul 13, 2017 at 5:20 PM, Rob Clark <robdclark@gmail.com> wrote:
>>> On Thu, Jul 13, 2017 at 1:35 AM, Sricharan R <sricharan@codeaurora.org> 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).
>>
>> I would like to understand whether there is a situation where an unmap is
>> called in atomic context without an enabled master?
>>
>> Let's say we have the case where all the unmap calls in atomic context happen
>> only from the master's context (in which case the device link should
>> take care of
>> the pm state of smmu), and the only unmap that happen in non-atomic context
>> is the one with master disabled. In such a case doesn it make sense to
>> distinguish
>> the atomic/non-atomic context and add pm_runtime_get_sync()/put_sync() only
>> for the non-atomic context since that would be the one with master disabled.
>>
>
> At least drm/msm needs to hold obj->lock (a mutex) in unmap, so it
> won't unmap anything in atomic ctx (but it can unmap w/ master
> disabled).  I can't really comment about other non-gpu drivers.  It
> seems like a reasonable constraint that either master is enabled or
> not in atomic ctx.
>
> Currently we actually wrap unmap w/ pm_runtime_get/put_sync(), but I'd
> like to drop that to avoid powering up the gpu.

Since the deferring the TLB maintenance doesn't look like the best approach [1],
how about if we try to power-up only the smmu from different client
devices such as,
GPU in the unmap path. Then we won't need to add pm_runtime_get/put() calls in
arm_smmu_unmap().

The client device can use something like - pm_runtime_get_supplier() since
we already have the device link in place with this patch series. This should
power-on the supplier (which is smmu) without turning on the consumer
(such as GPU).

pm_runtime_get_supplier() however is not exported at this moment.
Will it be useful to export this API and use it in the drivers.

Adding Rafael J. Wysocki for suggestions on pm_runtime_get_suppliers() API.


[1] https://patchwork.kernel.org/patch/9876489/


Best regards
Vivek

>
> BR,
> -R
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