linux-kernel - RE: [PATCH v5 7/7] iommu/exynos: Use device dependency links to control runtime pm

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Date:   Tue, 25 Oct 2016 12:23:10 +0530
From:   "Sricharan" <sricharan@...eaurora.org>
To:     "'Marek Szyprowski'" <m.szyprowski@...sung.com>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <iommu@...ts.linux-foundation.org>,
        <linux-samsung-soc@...r.kernel.org>
Cc:     "'Tomeu Vizoso'" <tomeu.vizoso@...labora.com>,
        "'Bartlomiej Zolnierkiewicz'" <b.zolnierkie@...sung.com>,
        "'Greg Kroah-Hartman'" <gregkh@...uxfoundation.org>,
        "'Kevin Hilman'" <khilman@...nel.org>,
        "'Rafael J. Wysocki'" <rjw@...ysocki.net>,
        "'Tomasz Figa'" <tomasz.figa@...il.com>,
        "'Krzysztof Kozlowski'" <krzk@...nel.org>,
        "'Inki Dae'" <inki.dae@...sung.com>,
        "'Tobias Jakobi'" <tjakobi@...h.uni-bielefeld.de>,
        "'Luis R. Rodriguez'" <mcgrof@...nel.org>,
        "'Kukjin Kim'" <kgene@...nel.org>,
        "'Mark Brown'" <broonie@...nel.org>,
        "'Lukas Wunner'" <lukas@...ner.de>
Subject: RE: [PATCH v5 7/7] iommu/exynos: Use device dependency links to control runtime pm

Hi Marek,

>>>>> diff --git a/drivers/iommu/exynos-iommu.c b/drivers/iommu/exynos-iommu.c
>>>>> index 5e6d7bbf9b70..59b4f2ce4f5f 100644
>>>>> --- a/drivers/iommu/exynos-iommu.c
>>>>> +++ b/drivers/iommu/exynos-iommu.c
>>>>> @@ -781,10 +781,6 @@ static void exynos_iommu_detach_device(struct iommu_domain *iommu_domain,
>>>>> 	if (!has_sysmmu(dev) || owner->domain != iommu_domain)
>>>>> 		return;
>>>>>
>>>>> -	list_for_each_entry(data, &owner->controllers, owner_node) {
>>>>> -		pm_runtime_put_sync(data->sysmmu);
>>>>> -	}
>>>>> -
>>>>> 	mutex_lock(&owner->rpm_lock);
>>>>>
>>>>> 	list_for_each_entry(data, &owner->controllers, owner_node) {
>>>>> @@ -848,10 +844,6 @@ static int exynos_iommu_attach_device(struct iommu_domain *iommu_domain,
>>>>>
>>>>> 	mutex_unlock(&owner->rpm_lock);
>>>>>
>>>>> -	list_for_each_entry(data, &owner->controllers, owner_node) {
>>>>> -		pm_runtime_get_sync(data->sysmmu);
>>>>> -	}
>>>>> -
>>>>> 	dev_dbg(dev, "%s: Attached IOMMU with pgtable %pa\n", __func__,
>>>>> 		&pagetable);
>>>>>
>>>>> @@ -1232,6 +1224,14 @@ static int exynos_iommu_of_xlate(struct device *dev,
>>>>>
>>>>> 	list_add_tail(&data->owner_node, &owner->controllers);
>>>>> 	data->master = dev;
>>>>> +
>>>>> +	/*
>>>>> +	 * SYSMMU will be runtime activated via device link (dependency) to its
>>>>> +	 * master device, so there are no direct calls to pm_runtime_get/put
>>>>> +	 * in this driver.
>>>>> +	 */
>>>>> +	device_link_add(dev, data->sysmmu, DL_FLAG_PM_RUNTIME);
>>>>> +
>>>>     So in the case of master with multiple sids, this would be called multiple times
>>>>     for the same master ?
>>> I don't know what is "multiple sids" case, but if given SYSMMU master
>>> device (supplier)
>>> has multiple SYSMMU controllers (consumers), then links will be created
>>> for each SYSMMU
>>> controller. Please note that this code is based on vanilla v4.9-rc1,
>>> which calls
>>> of_xlate() callback only once for every iommu for given master device.
>>> Your IOMMU
>>> deferred probe patches change this, but I already posted a fix for
>>> Exynos IOMMU driver
>>> to handle such case.
>>   By multiple sids, i meant iommus = <&phandle sid1 sid2 .. sidn> case,
>>   so xlate would be called multiples for the same master without deferred
>>   probing also. But the fix that you showed on the other thread would work
>>   here as well or maybe if you dont have masters with multiple sids you wont
>>   have any issues as well.
>
>Exynos SYSMMU driver always use "#iommu-cells = <0>", so it doesn't support
>multiple sids. However there is a case with 2 SYSMMU controllers attached
>to the same master device: "iommus = <&sysmmu_mfc_l>, <&sysmmu_mfc_r>;".
>
   with iommu-cells = <0> always, its ok. The case of 2 SYSMMU controllers that
   is shown above is fine, as anyways both the suppliers (symmu) needs to linked
    seperately. So it looks all fine.

Regards,
  Sricharan