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

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Date:   Mon, 16 Jul 2018 17:16:31 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     "Rafael J. Wysocki" <rafael@...nel.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 7/16/2018 2:25 PM, Rafael J. Wysocki wrote:
> 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?

The fact that currently we handle clocks only through runtime pm callbacks,
would it be better to call runtime pm put/get in system-wide PM callbacks.
This would be same as i mentioned in the other thread.

Best regards
Vivek

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