linux-kernel - Re: [RFC PATCH 2/2] iommu: rockchip: Handle system-wide and runtime PM

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Date:	Thu, 11 Dec 2014 16:22:57 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Tomasz Figa <tfiga@...omium.org>
Cc:	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	iommu@...ts.linux-foundation.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Heiko Stuebner <heiko@...ech.de>,
	Joerg Roedel <joro@...tes.org>,
	Kevin Hilman <khilman@...aro.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Daniel Kurtz <djkurtz@...omium.org>
Subject: Re: [RFC PATCH 2/2] iommu: rockchip: Handle system-wide and runtime PM

On 11 December 2014 at 13:42, Tomasz Figa <tfiga@...omium.org> wrote:
> Hi Ulf,
>
> On Thu, Dec 11, 2014 at 8:58 PM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> On 11 December 2014 at 09:26, Tomasz Figa <tfiga@...omium.org> wrote:
>>> This patch modifies the rockchip-iommu driver to consider state of
>>> the power domain the IOMMU is located in. When the power domain
>>> is powered off, the IOMMU cannot be accessed and register programming
>>> must be deferred until the power domain becomes enabled.
>
> [snip]
>
>>> @@ -988,11 +1107,28 @@ static int rk_iommu_probe(struct platform_device *pdev)
>>>                 return -ENXIO;
>>>         }
>>>
>>> +       pm_runtime_no_callbacks(dev);
>>> +       pm_runtime_enable(dev);
>>> +
>>> +       /* Synchronize state of the domain with driver data. */
>>> +       pm_runtime_get_sync(dev);
>>> +       iommu->is_powered = true;
>>
>> Doesn't the runtime PM status reflect the value of "is_powered", thus
>> why do you need to have a copy of it? Could it perpahps be that you
>> try to cope with the case when CONFIG_PM is unset?
>>
>
> It's worth noting that this driver fully relies on status of other
> devices in the power domain the IOMMU is in and does not enforce the
> status on its own. So in general, as far as my understanding of PM
> runtime subsystem, the status of the IOMMU device will be always
> suspended, because nobody will call pm_runtime_get() on it (except the
> get and put pair in probe). So is_powered is here to track status of
> the domain, not the device. Feel free to suggest a better way, though.

I see, thanks for clarifying. I think it makes sense as is, I have no
better suggestion.

Kind regards
Uffe
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