linux-kernel - Re: [PATCH v12 3/4] iommu/arm-smmu: Add the device

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Date:   Mon, 16 Jul 2018 10:55:44 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "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>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Rob Clark <robdclark@...il.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Tomasz Figa <tfiga@...omium.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>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Lukas Wunner <lukas@...ner.de>
Subject: Re: [PATCH v12 3/4] iommu/arm-smmu: Add the device_link between
 masters and smmu

On Thu, Jul 12, 2018 at 2:41 PM, Vivek Gautam
<vivek.gautam@...eaurora.org> wrote:
> Hi Rafael,
>
>
> On Wed, Jul 11, 2018 at 4:06 PM, Vivek Gautam
> <vivek.gautam@...eaurora.org> wrote:
>> Hi Rafael,
>>
>>
>>
>> On 7/11/2018 3:23 PM, Rafael J. Wysocki wrote:
>>>
>>> On Sunday, July 8, 2018 7:34:12 PM CEST 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>
>>>> Cc: Rafael J. Wysocki <rjw@...ysocki.net>
>>>> Cc: Lukas Wunner <lukas@...ner.de>
>>>> ---
>>>>
>>>>   - Change since v11
>>>>     * Replaced DL_FLAG_AUTOREMOVE flag with DL_FLAG_AUTOREMOVE_SUPPLIER.
>>>>
>>>>   drivers/iommu/arm-smmu.c | 12 ++++++++++++
>>>>   1 file changed, 12 insertions(+)
>>>>
>>>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>>>> index 09265e206e2d..916cde4954d2 100644
>>>> --- a/drivers/iommu/arm-smmu.c
>>>> +++ b/drivers/iommu/arm-smmu.c
>>>> @@ -1461,8 +1461,20 @@ static int arm_smmu_add_device(struct device *dev)
>>>>         iommu_device_link(&smmu->iommu, dev);
>>>>   +     if (pm_runtime_enabled(smmu->dev) &&
>>>
>>> Why does the creation of the link depend on whether or not runtime PM
>>> is enabled for the MMU device?
>>
>>
>> The main purpose of this device link is to handle the runtime PM
>> synchronization
>> between the supplier (iommu) and consumer (client devices, such as
>> GPU/display).
>> Moreover, the runtime pm is conditionally enabled for smmu devices that
>> support
>> such [1].
>
> Is there something you would like me to modify in this patch?

Not really, as long as you are sure that it is correct. :-)

You need to remember, however, that if you add system-wide PM
callbacks to the driver, the ordering between them and the client
device callbacks during system-wide suspend matters as well.  Don't
you need the link the ensure the correct system-wide suspend ordering
too?