Re: [PATCH v12 3/4] iommu/arm-smmu: Add the device_link between masters and smmu

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

On 7/17/2018 1:16 PM, Rafael J. Wysocki wrote:
> On Mon, Jul 16, 2018 at 1:46 PM, Vivek Gautam
> <vivek.gautam@codeaurora.org> wrote:
>>
>> On 7/16/2018 2:25 PM, Rafael J. Wysocki wrote:
>>> On Thu, Jul 12, 2018 at 2:41 PM, Vivek Gautam
>>> <vivek.gautam@codeaurora.org> wrote:
>>>> Hi Rafael,
>>>>
>>>>
>>>> On Wed, Jul 11, 2018 at 4:06 PM, Vivek Gautam
>>>> <vivek.gautam@codeaurora.org> wrote:
>>>>> Hi Rafael,
>>>>>
>>>>>
>>>>>
>>>>> On 7/11/2018 3:23 PM, Rafael J. Wysocki wrote:
>>>>>> On Sunday, July 8, 2018 7:34:12 PM CEST Vivek Gautam wrote:
>>>>>>> From: Sricharan R <sricharan@codeaurora.org>
>>>>>>>
>>>>>>> Finally add the device link between the master device and
>>>>>>> smmu, so that the smmu gets runtime enabled/disabled only when the
>>>>>>> master needs it. This is done from add_device callback which gets
>>>>>>> called once when the master is added to the smmu.
>>>>>>>
>>>>>>> Signed-off-by: Sricharan R <sricharan@codeaurora.org>
>>>>>>> Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
>>>>>>> Reviewed-by: Tomasz Figa <tfiga@chromium.org>
>>>>>>> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
>>>>>>> Cc: Lukas Wunner <lukas@wunner.de>
>>>>>>> ---
>>>>>>>
>>>>>>>     - Change since v11
>>>>>>>       * Replaced DL_FLAG_AUTOREMOVE flag with
>>>>>>> DL_FLAG_AUTOREMOVE_SUPPLIER.
>>>>>>>
>>>>>>>     drivers/iommu/arm-smmu.c | 12 ++++++++++++
>>>>>>>     1 file changed, 12 insertions(+)
>>>>>>>
>>>>>>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>>>>>>> index 09265e206e2d..916cde4954d2 100644
>>>>>>> --- a/drivers/iommu/arm-smmu.c
>>>>>>> +++ b/drivers/iommu/arm-smmu.c
>>>>>>> @@ -1461,8 +1461,20 @@ static int arm_smmu_add_device(struct device
>>>>>>> *dev)
>>>>>>>           iommu_device_link(&smmu->iommu, dev);
>>>>>>>     +     if (pm_runtime_enabled(smmu->dev) &&
>>>>>> Why does the creation of the link depend on whether or not runtime PM
>>>>>> is enabled for the MMU device?
>>>>>
>>>>> The main purpose of this device link is to handle the runtime PM
>>>>> synchronization
>>>>> between the supplier (iommu) and consumer (client devices, such as
>>>>> GPU/display).
>>>>> Moreover, the runtime pm is conditionally enabled for smmu devices that
>>>>> support
>>>>> such [1].
>>>> Is there something you would like me to modify in this patch?
>>> Not really, as long as you are sure that it is correct. :-)
>>>
>>> You need to remember, however, that if you add system-wide PM
>>> callbacks to the driver, the ordering between them and the client
>>> device callbacks during system-wide suspend matters as well.  Don't
>>> you need the link the ensure the correct system-wide suspend ordering
>>> too?
>>
>> The fact that currently we handle clocks only through runtime pm callbacks,
>> would it be better to call runtime pm put/get in system-wide PM callbacks.
>> This would be same as i mentioned in the other thread.
> Well, my point is that there's no reason for system-wide suspend to
> depend directly on runtime PM (which can be effectively disabled by
> user space as mentioned for multiple times in this thread).
>
> It simply is not efficient to let the clock run while the system as a
> whole is sleeping (even if power/control has been set to "on" for this
> particular device) and it should not be too hard to prevent that from
> happening.  You may need an additional flag in the driver for that or
> similar, but it definitely should be doable.

Right, I will modify the things are required. Thanks again for pointing 
this out.

Best regards
Vivek

>
> Now, that's my advice and I'm not the maintainer of that code, so it
> is your call (as long as the maintainer agrees with it).
>
> Thanks,
> Rafael