[U-Boot] [PATCH 2/2] [rfc] support booting arm64 android image

[Tom Rini]

On Wed, Jul 19, 2017 at 12:44:48PM +1000, Bin Chen wrote:
> On 18 July 2017 at 22:32, Tom Rini <trini at konsulko.com> wrote:
> 
> > On Thu, Jul 13, 2017 at 05:33:08PM +1000, Bin Chen wrote:
> > > Hi Tom,
> > >
> > > Thanks for the review.
> > >
> > > On 13 July 2017 at 04:25, Tom Rini <trini at konsulko.com> wrote:
> > >
> > > > On Tue, Jul 11, 2017 at 03:56:04PM +1000, Bin Chen wrote:
> > > >
> > > > > It's my understanding that we are supposed to use booti, instead of
> > > > bootm,
> > > > > for arm64 image. But booti lacks of android image support. Bootm has
> > > > > the andriod image support but lack of the arm64 image handling.
> > > > >
> > > > > So, what is suppose the right way of booting an android arm64 image?
> > > > > or, should we create a separate command?
> > > > >
> > > > > This patch is an invitation for that discussion.
> > > > >
> > > > > It *hacked* the booti command and it aslo assume the dtb is in the
> > > > second area
> > > > > of android boot image. It also has other belives like u-boot should
> > be
> > > > > in control of where to put the kernnel/ramdisk/dtb images so it
> > ignores
> > > > > the value specified in the android images.
> > > > >
> > > > > Signed-off-by: Bin Chen <bin.chen at linaro.org>
> > > >
> > > > So, booti is very much for the "Image" format described in the Linux
> > > > kernel in Documentation/arm64/booting.txt.  One can (and people have)
> > > > used bootm on aarch64 for "uImage" style kernels and FIT kernels, and I
> > > > would see being able to boot an aarch64 Android image with bootm as the
> > > > way to go forward.
> > >
> > >
> > > Are you suggesting that we should use bootm path, instead of booti?
> > >
> > > I have two questions regarding this:
> > >
> > > 1. currently arm64 kernel don't have a uImage kernel target. And I'm not
> > > sure
> > >  if adding that will be something that is wanted and/or sensible.
> >
> > There's some confusion here.  bootm is not only for "uImage" kernels.
> > It for example handles the aarch32 Android image format.
> >
> > > 2. bootm path doesn't have the logic that is currently in the booti, such
> > > as the
> > > kernel relocation.
> >
> > Now I'm confused, what is different in an "Android" image for aarch64
> > than from a standard aarch64 Linux kernel 'Image' ?
> >
> 
> Android image wraps the 'Image'. There is a section called “kernel” in
> Android
> image, and will place the Image there [1]. Do you think it is the right way
> to do that?
> 
> I think that's the case for aarch32 android image as well, but replace the
> 'Image' with
> aarch32 kernel build target - I don't know what the format of that target
> is.
> 
> [1]
> https://android.googlesource.com/platform/system/core/+/master/mkbootimg/bootimg.h
> 
> 
> > > Also, one other question raised during internal discussion was why the
> > > booti
> > > was created in the first place, if we could have had that implemented in
> > > the
> > > bootm path.
> >
> > Well, there's some discussion in the archives about this.  The short
> > answer is that "bootm" wasn't supposed to become a "figure out whatever
> > this image is, boot it" command.
> >
> 
> Good to know the idea beyond that and what bootm isn't supposed to be.
> That helps to decide whether we should stuff things into bootm or having a
> separate one.
> 
> 
> > In hindsight, now, I'm thinking that the aarch32 Android image support
> > maybe should have gone into "bootandroid" and in turn it would be easier
> > to get someone to write a new command, say "bootauto" that would ask
> > bootm/bootelf/bootefi/bootandroid/bootz/booti/etc if it liked the image
> > found at $address and if so, boot it, and if not, move on to checking
> > the next type.
> >
> 
> That seems the idea what many people agree upon. Not sure how easy
> to move aarch32 support out and I don't have a aarch32 platform to test.
> Do you think we'll want to start with aarch64 (considering that may be the
> aarch
> for most android phone out there) and have a separate boota(ndroid) command?

I think the best path forward today is to make sure that whatever
aarch64-Image support code that's needed from cmd/booti.c is available
so that 'bootm' can see that we have an Android-style image and then
further that we have an Image underneath it, rather than a zImage, and
handle running it appropriately.  I think bootm, aka "boot application
image from memory" is the best place to handle both 32 and 64bit Android
style images, as things stand today, at least.

-- 
Tom
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