[U-Boot] [PATCH] ARM: mx6: Enable MMC FS boot support

[Tom Rini]

On Wed, Apr 27, 2016 at 08:06:24PM -0500, Robert Nelson wrote:
> On Wed, Apr 27, 2016 at 7:54 PM, Tom Rini <trini at konsulko.com> wrote:
> 
> > On Thu, Apr 28, 2016 at 02:02:05AM +0200, Marek Vasut wrote:
> > > On 04/28/2016 01:49 AM, Robert Nelson wrote:
> > [snip]
> > > > 1:
> > > >
> > > > Yeap, end users like to delete "MLO/u-boot.img" that was in the "fat"
> > > > boot partition in our production beaglebone images specifically
> > > > "2014-05-14"  which was shipped by default on rev C.  Thus
> > > > soft-bricking/etc boards..
> > >
> > > OK, so because hypothetical user is an idiot, we should use sub-par
> > > solution ? User can also be an idiot and generate U-Boot which is over 1
> > > MiB, in which case I will turn your argument around against you. Sorry,
> > > I am not buying this.
> >
> > No, real users.  Lots of them.  From nearly every "community" oriented
> > board ever.  Which is why the distros also go for this method, point #2.
> >
> > > > http://beagleboard.org/latest-images
> > > >
> > > > Moving it under the 1MB location, has solved that problem.
> > >
> > > Until u-boot grows over 1 MiB. This only postponed the problem.
> > > Since there is filesystem support in the SPL, we should use that
> > > as a superior solution which doesn't suffer from this problem.
> >
> > I thought people were supposed to be aligning their first partitions
> > much higher these days, 4MiB? as the general case for being safe
> > regardless of the actual flash in the SD card.  Setting aside sandbox
> > which I hope grows extremely large for testing purposes, I really hope
> > U-Boot + SPL can always stay under 1MiB.  Our job is to boot the next
> > stage.  If we get so large in our design of implementing things that we
> > forget this, we have a problem.
> >
> 
> I've followed the 4kb convention and fdisk defaults to 1MB offset: (even
> thou we aren't dealing spinning disks)
> 
> https://www.ibm.com/developerworks/library/l-linux-on-4kb-sector-disks/
> 
> I haven't looked at the latest eMMC spec, but the eMMC 'boot' sections on
> current silicon is only 1MB (x2)
> 
> mmcblk1boot0 179:16   0    1M  1 disk
> mmcblk1boot1 179:24   0    1M  1 disk
> mmcblk1      179:8    0  1.8G  0 disk

eMMC is "different" since you don't partition the boot sections usually,
so offset of 0 is good.  But for the eMMC itself when you do partition
it I'd have sworn 4MiB was what to align on.  I haven't thrown
flashbench on something in a while however...

-- 
Tom
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