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

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Date:   Tue, 8 Jun 2021 20:07:05 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        Al Cooper <alcooperx@...il.com>
Cc:     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 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).
-- 
Florian