linux-kernel - Re: [PATCH 2/2] mmc: sdhci-iproc: Add support for the legacy sdhci controller on the BCM7211

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Message-ID: <CAPDyKFpEtvjS1mWC68gRBWD64dq2M1LO84UWE5uDLTzbGz1g8Q@mail.gmail.com>
Date:   Wed, 9 Jun 2021 11:22:15 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Al Cooper <alcooperx@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        DTML <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Ray Jui <rjui@...adcom.com>, Rob Herring <robh+dt@...nel.org>,
        Scott Branden <sbranden@...adcom.com>
Subject: Re: [PATCH 2/2] mmc: sdhci-iproc: Add support for the legacy sdhci
 controller on the BCM7211

On Wed, 9 Jun 2021 at 05:07, Florian Fainelli <f.fainelli@...il.com> wrote:
>
>
>
> On 6/8/2021 5:40 AM, Ulf Hansson wrote:
> > On Wed, 2 Jun 2021 at 21:28, Al Cooper <alcooperx@...il.com> wrote:
> >>
> >> Add support for the legacy Arasan sdhci controller on the BCM7211 and
> >> related SoC's. This includes adding a .shutdown callback to increase
> >> the power savings during S5.
> >
> > Please split this into two separate changes.
> >
> > May I also ask about the ->shutdown() callback and in relation to S5.
> > What makes the ->shutdown callback only being invoked for S5?
>
> It is not only called for S5 (entered via poweroff on a prompt) but also
> during kexec or reboot. The poweroff path is via:
>
> kernel_power_off() -> kernel_shutdown_prepare() -> device_shutdown() ->
> .shutdown()
>
> For kexec or reboot we do not really care about power savings since we
> are about to load a new image anyway, however for S5/poweroff we do care
> about quiescing the eMMC controller in a way that its clocks and the
> eMMC device can be put into low power mode since we will stay in that
> mode for seconds/hours/days until someone presses a button on their
> remote (or other wake-up sources).

Hmm, I am not sure I understand correctly. At shutdown we don't care
about wake-up sources from the kernel point of view, instead we treat
everything as if it will be powered off.

We put devices into low power state at system suspend and potentially
also during some of the hibernation phases.

Graceful shutdown of the eMMC is also managed by the mmc core.

Kind regards
Uffe