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

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

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?

Best regards
Vivek

>>
>>
>> What about system-wide PM and system shutdown?  Are they always guaranteed
>> to happen in the right order without the link?
>
>
> When there's no runtime PM, there's no clocks, and other resources to be
> handled.
> So, we don't need device link for system-wide PM and system shutdown to work
> correctly.
> That's the case with current arm-smmu driver.
> Is it something that i am missing here?
>
> [1] https://lkml.org/lkml/2018/3/8/775
>
> Thanks
> Vivek
>>>
>>> +           !device_link_add(dev, smmu->dev,
>>> +                       DL_FLAG_PM_RUNTIME |
>>> DL_FLAG_AUTOREMOVE_SUPPLIER)) {
>>> +               dev_err(smmu->dev, "Unable to add link to the consumer
>>> %s\n",
>>> +                       dev_name(dev));
>>> +               ret = -ENODEV;
>>> +               goto out_unlink;
>>> +       }
>>> +
>>>         return 0;
>>>   +out_unlink:
>>> +       iommu_device_unlink(&smmu->iommu, dev);
>>> +       arm_smmu_master_free_smes(fwspec);
>>>   out_cfg_free:
>>>         kfree(cfg);
>>>   out_free:
>>>
>>
>
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