Re: [PATCH] mmc: Move the mmc driver init earlier

[Feng Tang]

Hi Greg,

Thanks for the prompt review.

On Tue, Aug 14, 2018 at 09:40:41AM +0200, Greg Kroah-Hartman wrote:
> On Tue, Aug 14, 2018 at 03:38:10PM +0800, Feng Tang wrote:
> > Hi Greg,
> > 
> > On Tue, Aug 14, 2018 at 09:18:34AM +0200, Greg Kroah-Hartman wrote:
> > > On Tue, Aug 14, 2018 at 02:39:59PM +0800, Feng Tang wrote:
> > > > Hi Greg, Ulf
> > > > 
> > > > Could you help to review this? many thanks!
> > > 
> > > Review what?  I see no patch here.  And why would I need to review a mmc
> > > patch in the middle of the merge window?
> > > 
> > > totally confused,
> > 
> > Sorry for the confusion! I didn't noticed the 4.19 merge window.
> > 
> > The patch was originally posted in June, and has gone through some
> > review discussions with mmc maintainers, my last mail was trying
> > to keep some discussion info.
> 
> Ok, then why ask me?  I'm not the mmc maintainer.

The reason is this patch not only touches the mmc, but also affects many other
subsystems in drivers/ as the init order is changed. And the get_maintainer.pl
shows you are the first suggested reviewer for changes to drivers/Makefile :)

> 
> > The original patch is:
> > -----
> > 
> > >From 1514c7d56e887ace37466dded09bc43f2a4c9a4a Mon Sep 17 00:00:00 2001
> > From: Feng Tang <feng.tang@xxxxxxxxx>
> > Date: Fri, 8 Jun 2018 17:10:30 +0800
> > Subject: [PATCH] mmc: Move the mmc driver init earlier
> > 
> > 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. And it should benefit other non-x86 platforms
> > which see the similar waiting for emmc rootfs.
> > 
> > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
> > ---
> >  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
> 
> Spelling error :)

Will change it.

> 
> > +obj-y				+= mmc/
> > +
> >  # tty/ comes before char/ so that the VT console is the boot-time
> >  # default.
> >  obj-y				+= tty/
> 
> Everyone wants to be first.  Watch out if you try to put stuff before
> tty, you have to be very careful.  There are sd serial devices, right?

As the eMMC/SD card initialization takes quite some time, the SDHCI
host controller's module init function will quickly return, while leaving 
a worker to do the real card detection/initialization, so other subsystems
should not be blocked.

And yes, it is safer to move it after tty/

> 
> Anyway, nothing we can do now until after 4.19-rc1 is out.

Understood, will send v2 after the merge window. Thanks again.

- Feng