linux-kernel - Re: [PATCH v8 4/5] iommu/arm-smmu: Add the device

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Date:   Thu, 8 Mar 2018 10:29:47 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <joro@...tes.org>,
        "robh+dt" <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Will Deacon <will.deacon@....com>,
        Rob Clark <robdclark@...il.com>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        devicetree@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        Tomasz Figa <tfiga@...omium.org>, jcrouse@...eaurora.org,
        Stephen Boyd <sboyd@...eaurora.org>,
        Sricharan R <sricharan@...eaurora.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Archit Taneja <architt@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v8 4/5] iommu/arm-smmu: Add the device_link between
 masters and smmu

On Wed, Mar 7, 2018 at 6:17 PM, Robin Murphy <robin.murphy@....com> wrote:
> On 02/03/18 10:10, Vivek Gautam wrote:
>>
>> From: Sricharan R <sricharan@...eaurora.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@...eaurora.org>
>> Signed-off-by: Vivek Gautam <vivek.gautam@...eaurora.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...

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;
>>
>



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