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

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Message-id: <bff28d5b-3b39-a5bb-b381-2d7626566a2d@samsung.com>
Date:   Mon, 24 Oct 2016 14:39:15 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Sricharan <sricharan@...eaurora.org>, 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 Sricharan,


On 2016-10-24 14:29, Sricharan wrote:
>>>> This patch uses recently introduced device dependency links to track the
>>>> runtime pm state of the master's device. This way each SYSMMU controller
>>>> is set to runtime active only when its master's device is active and can
>>>> restore or save its state instead of being activated all the time when
>>>> attached to the given master device. This way SYSMMU controllers no longer
>>>> prevents respective power domains to be turned off when master's device
>>>> is not being used.
>>>>
>>>> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
>>>> ---
>>>> drivers/iommu/exynos-iommu.c | 16 ++++++++--------
>>>> 1 file changed, 8 insertions(+), 8 deletions(-)
>>>>
>>>> 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>;".

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland