Re: [PATCH v8 4/5] iommu/arm-smmu: Add the device_link between masters and smmu

[Vivek Gautam <vivek.gautam-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On Wed, Mar 7, 2018 at 6:17 PM, Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org> wrote:
> On 02/03/18 10:10, Vivek Gautam wrote:
>>
>> From: Sricharan R <sricharan-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.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-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
>> Signed-off-by: Vivek Gautam <vivek.gautam-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
>> ---
>>   drivers/iommu/arm-smmu.c | 21 +++++++++++++++++++++
>>   1 file changed, 21 insertions(+)
>>
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index 3d6a1875431f..bb1ea82c1003 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -217,6 +217,9 @@ struct arm_smmu_device {
>>         /* IOMMU core code handle */
>>         struct iommu_device             iommu;
>> +
>> +       /* runtime PM link to master */
>> +       struct device_link *link;
>
>
> Just the one?
>
>>   };
>>     enum arm_smmu_context_fmt {
>> @@ -1470,10 +1473,26 @@ static int arm_smmu_add_device(struct device *dev)
>>         iommu_device_link(&smmu->iommu, dev);
>>   +     /*
>> +        * Establish the link between smmu and master, so that the
>> +        * smmu gets runtime enabled/disabled as per the master's
>> +        * needs.
>> +        */
>> +       smmu->link = device_link_add(dev, smmu->dev, DL_FLAG_PM_RUNTIME);
>
>
> Maybe I've misunderstood how the API works, but AFAICS the second and
> subsequent devices are all just going to overwrite (and leak) the link of
> the previous one...

Also, noticed one more thing while testing on sdm845. When we are
conditionally enabling the runtime pm, we should create the device
link too conditionally, i.e. only in the case the smmu->dev has
runtime pm_enabled we can create this device link between smmu and the
master device.
Otherwise when the master tries to do a pm_runtime_get() over itself,
the device link will ensure that pm_runtime_get() for smmu is done
first. But that will fail when we don't have pm runtime enabled over
smmu, and so the master device's pm_runtime_get() will fail too.
Will fix this in the next version.

Thanks
Vivek

>
>> +       if (!smmu->link) {
>> +               dev_warn(smmu->dev, "Unable to create device link between
>> %s and %s\n",
>> +                        dev_name(smmu->dev), dev_name(dev));
>> +               ret = -ENODEV;
>> +               goto out_unlink;
>> +       }
>> +
>>         arm_smmu_rpm_put(smmu);
>>         return 0;
>>   +out_unlink:
>> +       iommu_device_unlink(&smmu->iommu, dev);
>> +       arm_smmu_master_free_smes(fwspec);
>>   out_rpm_put:
>>         arm_smmu_rpm_put(smmu);
>>   out_cfg_free:
>> @@ -1496,6 +1515,8 @@ static void arm_smmu_remove_device(struct device
>> *dev)
>>         cfg  = fwspec->iommu_priv;
>>         smmu = cfg->smmu;
>>   +     device_link_del(smmu->link);
>
>
> ...and equivalently you end up with a double-free (or more) here of a link
> which may not have belonged to dev anyway.
>
> Robin.
>
>
>> +
>>         ret = arm_smmu_rpm_get(smmu);
>>         if (ret < 0)
>>                 return;
>>
>



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