[U-Boot] Unified u-boot feature set for simpler distro support

[Tom Rini]

On Mon, Aug 05, 2013 at 03:09:55PM -0600, Stephen Warren wrote:
> On 08/05/2013 03:00 PM, Tom Rini wrote:
> > On Mon, Aug 05, 2013 at 02:49:58PM -0600, Stephen Warren wrote:
> >> On 08/05/2013 02:43 PM, Wolfgang Denk wrote: ...
> >>> Please look into Tom's proposal to got the SPL / Falcon mode
> >>> way. I fully agre with him there.
> >> 
> >> From my reading of doc/README.falcon, in order to use it, you
> >> still must set everything up in order to do a full non-falcon
> >> boot, and then simply save a serialized version of the
> >> zImage/DTB/bootargs/... using a special U-Boot command.
> > 
> > You must setup a certain amount of things, yes.  And from what
> > you've documented in the i2c thread about the Tegra orer, it
> > depends a bit on the SoC.
> > 
> > [snip]
> >> And also, if a distro installs an updated kernel, how does it
> >> tell U-Boot to invalidate the previously serialized data that
> >> falcon mode uses to boot, and re-create it using the new kernel
> >> image?
> > 
> > Dirty "secret" time, with device trees, it's just the device tree
> > we loaded, with whatever run-time fixups are done.  Doing this from
> > the Linux side is a solvable problem.
> 
> Oh! Where does the zImage binary come from then? The documentation
> explicitly says it's written to flash by "spl export", and I assume
> that's so that the SPL (that's executing falcon mode) doesn't have to
> initialize SD card drivers, filesystems, etc. in order to load the
> zImage from the card, but rather simply a single flash driver to read
> the exported image. If falcon mode has to do all that, why is it any
> faster than the main U-Boot doing exactly the same?

'spl export' sets up the args blob that would be used, for ATAGs or the
ready to go device tree.  The time savings depends on how long (or, how
quickly) your platform goes from power on to U-Boot asking you to
interrupt auto-boot.  When we were talking about this last year at the
developers meeting, it didn't seem like a big deal to some platforms
that Simon Glass had as they come up quickly.  On others (like say
beaglebone) skipping out on probing various things in U-Boot is a time
win.

-- 
Tom
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