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

[Vivek Gautam]

On Thu, Mar 8, 2018 at 10:29 AM, Vivek Gautam
<vivek.gautam@xxxxxxxxxxxxxx> wrote:
> On Wed, Mar 7, 2018 at 6:17 PM, Robin Murphy <robin.murphy@xxxxxxx> wrote:
>> On 02/03/18 10:10, 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>
>>> ---
>>>   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?

we will either have to count all the devices that are present on the
iommu bus, or
maintain a list to which all the links can be added.
But to add the list, we will have to initialize a LIST_HEAD in struct
device_link
as well.

Or, I think we don't even need to maintain a pointer to link with smmu.
In arm_smmu_remove_device(), we can find out the correct link, and delete it.

        list_for_each_entry(link, &dev->links.suppliers, c_node)
                if (link->supplier == smmu->dev);
                           device_link_del(link);

Should that be fine?

Rafael, does the above snippet looks right to you? Context: smmu->dev
is the supplier, and dev is the consumer. We want to find the link,
and delete it.

regards
Vivek

>>
>>>   };
>>>     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...
>
> Sorry, my bad. Will take care of this.
>
> regards
> 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;
>>>
>>
>
>
>
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> of Code Aurora Forum, hosted by The Linux Foundation



-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation