linux-kernel - Re: [PATCH] mmc: Move the mmc driver init earlier

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Message-ID: <CAPDyKFrs3ngkVVQaq34V9qzV3KoFdy=B+UbLnzR=fHKsOco=tg@mail.gmail.com>
Date:   Tue, 12 Jun 2018 08:25:44 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH] mmc: Move the mmc driver init earlier

On 8 June 2018 at 11:51, Feng Tang <feng.tang@...el.com> wrote:
> When doing some boot time optimization for an eMMC rootfs NUCs,
> we found the rootfs may spend around 100 microseconds waiting
> for eMMC card to be initialized, then the rootfs could be
> mounted.
>         [    1.216561] Waiting for root device /dev/mmcblk1p1...
>         [    1.289262] mmc1: new HS400 MMC card at address 0001
>         [    1.289667] mmcblk1: mmc1:0001 R1J56L 14.7 GiB
>         [    1.289772] mmcblk1boot0: mmc1:0001 R1J56L partition 1 8.00 MiB
>         [    1.289869] mmcblk1boot1: mmc1:0001 R1J56L partition 2 8.00 MiB
>         [    1.289967] mmcblk1rpmb: mmc1:0001 R1J56L partition 3 4.00 MiB
>         [    1.292798]  mmcblk1: p1 p2 p3
>         [    1.300576] EXT4-fs (mmcblk1p1): couldn't mount as ext3 due to feature incompatibilities
>         [    1.300912] EXT4-fs (mmcblk1p1): couldn't mount as ext2 due to feature incompatibilities
>
> And this is a common problem for smartphones, tablets, embedded
> devices and automotive products. This patch will make the eMMC/SD
> card  start initializing earlier, by changing its order in drivers/Makefile.
>
> On our platform, the waiting for eMMC card is almost eliminated with the patch,
> which is critical to boot time.

I am wondering what kernel version you are running here. There have
been some changes to the mmc initialization path, which perhaps can
help.

>
> Signed-off-by: Feng Tang <feng.tang@...el.com>
> ---
>  drivers/Makefile | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/Makefile b/drivers/Makefile
> index 24cd47014657..c473afd3c688 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -50,6 +50,9 @@ obj-$(CONFIG_REGULATOR)               += regulator/
>  # reset controllers early, since gpu drivers might rely on them to initialize
>  obj-$(CONFIG_RESET_CONTROLLER) += reset/
>
> +# put mmc early as many morden devices use emm/sd card as rootfs storage
> +obj-y                          += mmc/
> +

Your suggested approach isn't really a solution, as it may work for
your particular case but not for everybody else.

>  # tty/ comes before char/ so that the VT console is the boot-time
>  # default.
>  obj-y                          += tty/
> @@ -128,7 +131,6 @@ obj-$(CONFIG_EISA)          += eisa/
>  obj-$(CONFIG_PM_OPP)           += opp/
>  obj-$(CONFIG_CPU_FREQ)         += cpufreq/
>  obj-$(CONFIG_CPU_IDLE)         += cpuidle/
> -obj-y                          += mmc/
>  obj-$(CONFIG_MEMSTICK)         += memstick/
>  obj-$(CONFIG_NEW_LEDS)         += leds/
>  obj-$(CONFIG_INFINIBAND)       += infiniband/
> --
> 2.14.1
>

Kind regards
Uffe