Re: [PATCH v12 3/4] iommu/arm-smmu: Add the device_link between masters and smmu

From: Vivek Gautam <vivek.gautam@codeaurora.org>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: joro@8bytes.org, robh+dt@kernel.org, mark.rutland@arm.com,
	robin.murphy@arm.com, will.deacon@arm.com,
	iommu@lists.linux-foundation.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, alex.williamson@redhat.com,
	robdclark@gmail.com, linux-pm@vger.kernel.org,
	freedreno@lists.freedesktop.org, sboyd@kernel.org,
	tfiga@chromium.org, sricharan@codeaurora.org,
	m.szyprowski@samsung.com, architt@codeaurora.org,
	linux-arm-msm@vger.kernel.org, jcrouse@codeaurora.org,
	Lukas Wunner <lukas@wunner.de>
Subject: Re: [PATCH v12 3/4] iommu/arm-smmu: Add the device_link between masters and smmu
Date: Wed, 11 Jul 2018 16:06:14 +0530	[thread overview]
Message-ID: <741cc78b-59a7-5289-e42f-1511ebedb15d@codeaurora.org> (raw)
In-Reply-To: <5179668.PHK6S3sxLu@aspire.rjw.lan>

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@codeaurora.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@codeaurora.org>
>> Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
>> Reviewed-by: Tomasz Figa <tfiga@chromium.org>
>> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
>> Cc: Lukas Wunner <lukas@wunner.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].
>
> What about system-wide PM and system shutdown?  Are they always guaranteed
> to happen in the right order without the link?

When there's no runtime PM, there's no clocks, and other resources to be 
handled.
So, we don't need device link for system-wide PM and system shutdown to 
work correctly.
That's the case with current arm-smmu driver.
Is it something that i am missing here?

[1] https://lkml.org/lkml/2018/3/8/775

Thanks
Vivek
>> +	    !device_link_add(dev, smmu->dev,
>> +			DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_SUPPLIER)) {
>> +		dev_err(smmu->dev, "Unable to add link to the consumer %s\n",
>> +			dev_name(dev));
>> +		ret = -ENODEV;
>> +		goto out_unlink;
>> +	}
>> +
>>   	return 0;
>>   
>> +out_unlink:
>> +	iommu_device_unlink(&smmu->iommu, dev);
>> +	arm_smmu_master_free_smes(fwspec);
>>   out_cfg_free:
>>   	kfree(cfg);
>>   out_free:
>>
>