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

[Rob Clark]

On Thu, Jul 13, 2017 at 9:53 AM, Sricharan R <sricharan@xxxxxxxxxxxxxx> wrote:
> Hi,
>
> On 7/13/2017 5:20 PM, Rob Clark wrote:
>> 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().
>
>  Ok, with that being the case, there are two things here,
>
>  1) If the device links are still intact at these places where unmap is called,
>     then pm_runtime from the master would setup the all the clocks. That would
>     avoid reintroducing the locking indirectly here.
>
>  2) If not, then doing it here is the only way. But for both cases, since
>     the unmap can be called from atomic context, resume handler here should
>     avoid doing clk_prepare_enable , instead move the clk_prepare to the init.
>

I do kinda like the approach Marek suggested.. of deferring the tlb
flush until resume.  I'm wondering if we could combine that with
putting the mmu in a stalled state when we suspend (and not resume the
mmu until after the pending tlb flush)?

BR,
-R