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

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Date:   Mon, 12 Mar 2018 15:51:44 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>, "robh+dt" <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Rob Clark <robdclark@...il.com>, 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 Fri, Mar 9, 2018 at 6:04 PM, Robin Murphy <robin.murphy@....com> wrote:
> On 09/03/18 07:11, Vivek Gautam wrote:
>>
>> On Thu, Mar 8, 2018 at 10:29 AM, Vivek Gautam
>> <vivek.gautam@...eaurora.org> wrote:
>>>
>>> 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?
>>
>>
>> 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.
>
>
> Actually, looking at the existing code, it seems like device_link_add() will
> in fact look up and return any existing link between a given supplier and
> consumer - is that intentional API behaviour that users may rely on to avoid
> keeping track of explicit link pointers?
> (or conversely, might it be
> reasonable to factor out a device_link_find() function?)

Yea, that sounds better.

regards
Vivek

>
> Robin.
>
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