linux-kernel - Re: [PATCH v9 4/5] iommu/arm-smmu: Add the device

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Date:   Thu, 15 Mar 2018 15:18:08 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Vivek Gautam <vivek.gautam@...eaurora.org>,
        Joerg Roedel <joro@...tes.org>,
        Rob Herring <robh+dt@...nel.org>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        devicetree@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Rob Clark <robdclark@...il.com>,
        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 v9 4/5] iommu/arm-smmu: Add the device_link between
 masters and smmu

On Thu, Mar 15, 2018 at 2:50 AM, Robin Murphy <robin.murphy@....com> wrote:
> On 13/03/18 08:55, 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>
>> Reviewed-by: Tomasz Figa <tfiga@...omium.org>
>> ---
>>   drivers/iommu/arm-smmu.c | 29 +++++++++++++++++++++++++++++
>>   1 file changed, 29 insertions(+)
>>
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index 56a04ae80bf3..64953ff2281f 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -1460,10 +1460,31 @@ static int arm_smmu_add_device(struct device *dev)
>>         iommu_device_link(&smmu->iommu, dev);
>>   +     if (pm_runtime_enabled(smmu->dev)) {
>> +               struct device_link *link;
>> +
>> +               /*
>> +                * Establish the link between smmu and master, so that the
>> +                * smmu gets runtime enabled/disabled as per the master's
>> +                * needs.
>> +                */
>> +               link = device_link_add(dev, smmu->dev,
>> DL_FLAG_PM_RUNTIME);
>> +               if (!link) {
>
>
> FWIW, given that we don't really care about link itself, I'd be quite happy
> to simplify that lot down to:
>
>         if (pm_runtime_enabled(smmu_dev) &&
>             !device_link_add(dev, smmu->dev, DL_FLAG_PM_RUNTIME)) {
>
>> +                       dev_warn(smmu->dev,
>> +                                "Unable to add link to the consumer
>> %s\n",
>> +                                dev_name(dev));
>
>
> (side note: since device_link_add() already prints a message on success,
> maybe it could print its own failure message too?)

I think we care whether adding the link succeeded. If it fails to be
added, we might end up with a complete system lockup on a system with
power domains.

Best regards,
Tomasz