[U-Boot] [PATCH 10/14] dm: mmc: sunxi: Add support for driver model

[Maxime Ripard]

Hi Simon,

On Fri, Jul 14, 2017 at 07:47:45AM -0600, Simon Glass wrote:
> On 5 July 2017 at 14:14, Maxime Ripard <maxime.ripard at free-electrons.com> wrote:
> > On Wed, Jul 05, 2017 at 04:57:40PM +0200, Maxime Ripard wrote:
> >> On Tue, Jul 04, 2017 at 01:33:25PM -0600, Simon Glass wrote:
> >> > Hi Maxime,
> >> >
> >> > On 21 June 2017 at 01:31, Maxime Ripard
> >> > <maxime.ripard at free-electrons.com> wrote:
> >> > > Hi Simon,
> >> > >
> >> > > On Mon, Jun 19, 2017 at 11:11:27AM -0600, Simon Glass wrote:
> >> > >> Add a driver-model version of this driver which mostly uses the existing
> >> > >> code. The old code can be removed once all boards are switched over.
> >> > >>
> >> > >> Signed-off-by: Simon Glass <sjg at chromium.org>
> >> > >
> >> > > I'm not sure if you tested that, but we have some code that switches
> >> > > the MMC indices when using both an eMMC and an external MMC.
> >> > >
> >> > > http://git.denx.de/?p=u-boot.git;a=blob;f=board/sunxi/board.c#l494
> >> > >
> >> > > This predates my time, but it seems that it was done to have a
> >> > > consistent boot MMC device ID.
> >> > >
> >> > > I'm not really sure we can get rid of it (even if it creates some
> >> > > issues of it's own), but what would be the impact of a switch to the
> >> > > device model on that logic?
> >> >
> >> > That is a pretty terrible hack.
> >>
> >> Yes, I know. This is especially bad when used together with other
> >> tools that rely on one MMC index for example (such as fastboot).
> >>
> >> I wanted to kill it for quite some time, but I'm a bit reluctant due
> >> to the possible side effects.
> >>
> >> > I'm not sure whether it will continue to work with DM. It does still
> >> > use the device number in the block device, so maybe...  Do you have
> >> > a board would use this?
> >>
> >> I guess I do. I'll give it a try or tonight and let you know.
> >
> > I just tested. Even with an eMMC (which was the first use case for
> > that hack), it works, even things that are not mainline yet (fastboot,
> > etc).
> >
> > It obviously break the old scripts relying on the mmc index, but I
> > guess that's ok.
> >
> > There's one regression though. Our eMMC will always be the second one,
> > which means that the distro bootargs will always boot on the external
> > SD first (which is always going to be mmc0).
> >
> > That's due to the fact that the eMMC controller is the third one, and
> > is thus probed last. We obviously want something deterministic for
> > fastboot for example, but booting partitions of the media you started
> > from make sense I guess. And this is what this hack was trying to
> > address.
> 
> OK...so what should we do here?

I guess we should just drop the hack. We'll have to at some point
anyway. But I guess we should also find a way to tweak the distro
bootcmd at boot time to search for the medium that we booted on first.

I'm not really sure how to do this though.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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