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

[Rafael J. Wysocki]

On Thu, Jul 12, 2018 at 2:41 PM, Vivek Gautam
<vivek.gautam@xxxxxxxxxxxxxx> wrote:
> Hi Rafael,
>
>
> On Wed, Jul 11, 2018 at 4:06 PM, Vivek Gautam
> <vivek.gautam@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
>>>>
>>>> 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@xxxxxxxxxxxxxx>
>>>> Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
>>>> Reviewed-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
>>>> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
>>>> Cc: Lukas Wunner <lukas@xxxxxxxxx>
>>>> ---
>>>>
>>>>   - 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?