linux-kernel - Re: [PATCH v4 2/2] iommu/exynos: Add proper runtime pm support

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Message-ID: <20161006173756.GK3296@wotan.suse.de>
Date:   Thu, 6 Oct 2016 19:37:56 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org,
        linux-samsung-soc@...r.kernel.org, Joerg Roedel <joro@...tes.org>,
        Inki Dae <inki.dae@...sung.com>, Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <k.kozlowski@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Mark Brown <broonie@...nel.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Lukas Wunner <lukas@...ner.de>,
        Kevin Hilman <khilman@...nel.org>,
        Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
Subject: Re: [PATCH v4 2/2] iommu/exynos: Add proper runtime pm support

On Thu, Sep 29, 2016 at 10:12:31AM +0200, Marek Szyprowski wrote:
> This patch uses recently introduced device links to track the runtime pm
> state of the master's device. This way each SYSMMU controller is runtime
> activated when its master's device is active 

instead of?

BTW what is the master device of a SYSMMU? I have no clue about these
IOMMU devices here.

> and can save/restore its state instead of being enabled all the time.

I take it this means currently even if the master device is disabled
(whatever that is) all SYSMMU controllers are kept enabled, is that right?
The issue here is this wastes power? Or what is the issue?

> This way SYSMMU controllers no
> longer prevents respective power domains to be turned off when master's
> device is not used.

So when the master device is idle we want to also remove power from the
controllers ? How much power does this save on a typical device in the
market BTW ?

> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>  drivers/iommu/exynos-iommu.c | 225 ++++++++++++++++++-------------------------
>  1 file changed, 94 insertions(+), 131 deletions(-)

I'm reviewing the device link patches now but since this is a demo of
use of that I'll note the changes here are pretty large and it makes
it terribly difficult for review. Is there any way this patch can be split
up in to logical atomic pieces that only do one task upon change ?

  Luis