[U-Boot] [PATCH 1/1]: environment in eMMC boot partition

[Sergey Kubushyn]

On Sat, 8 Oct 2016, Tom Rini wrote:

> On Wed, Oct 05, 2016 at 01:28:07PM -0700, Sergey Kubushyn wrote:
>
>> This allows to place U-Boot environment into eMMC boot partition thus
>> saving space on user partition for the OS (or whatever.) When booting
>> off of eMMC many (all?) MCUs can use dedicated boot0/boot1 partitions
>> to boot so U-Boot (or SPL) is written to one (or both) such partitions.
>> When such boot configuration is used it makes sense to place environment
>> in the same partition where the U-Boot itself is so the entire user
>> partition is available for the OS.
>>
>> It might be not well polished yet but it is a simple patch that can be
>> reworked later.
>>
>> It uses 4 Kconfig variables right now which probably belong to the board
>> Kconfig. Those are:
>>
>> CONFIG_ENV_IN_EMMC_BOOT -- tells that environment is in eMMC boot
>>  partition if defined
>>
>> CONFIG_EMMC_ENV_PART -- tells which boot partition environment should be
>>  stored in (either 1 or 2)
>>
>> CONFIG_EMMC_BOOT_PART -- which boot partition will be used by eMMC to
>>  read U-Boot/SPL binary for boot protocol (either 1 or 2.) That can be
>>  different from the environment partition
>>
>> CONFIG_EMMC_BOOT_ACK -- tells that eMMC should provide boot ACKs if
>>  defined
>>
>> Here is an excerpt from actual board Kconfig:
>
> I think what's missing is that in the other cases where we do
> environment in the eMMC boot partitions we don't need the boot ack part.
> Can you see if the existing hooks work, when you add in something for
> boot ack?

Eh, I _DO_ use existing hook. And one of the parameters passed to that
hook is boot ack (drivers/mmc/mmc_boot.c, line 101):

=== Cut ===
int mmc_set_part_conf(struct mmc *mmc, u8 ack, u8 part_num, u8 access)
=== Cut ===

I could've just set it to 0 unconditionally but there might be some board
configs that might require it to be enabled so I made it configurable.

And I don't think we have any boards with environment in boot partition
because there is simply no support for this in common/enc_mmc.c. Remember,
eMMC boot partition and a partition on eMMC you boot off of are totally
orthogonal :) Boot partitions (there are 2 of those and one user partition
on eMMC) are special. You have to explicitely switch to a boot partition
to access it. When U-Boot is started eMMC boot partition it had been read
off (if the system boots off of boot partition using special boot protocol)
is long gone and what U-Boot sees is _USER_ partition. One can create
up to 4 GP partitions on eMMC but those are _DIFFERENT_ partitions and
they all reside in _USER_ partition i.e. GP partitions just subdivide the
single _USER_ partition into up to 4 parts.

When you boot off of an eMMC boot partition U-Boot binary is written into
boot partition so no part of visible _USER_ partition is taken, not a
single byte. That means that only one 512-byte block of the user partition
is reserved (MBR/partition table) so one can start a primary DOS partition
on eMMC at block 1 and use the entire space up to the last block for that
partition. However there is still U-Boot environment that one has to put
somewhere. Although it is possible to put it into user partition starting
first DOS (or GP) partition at e.g. block 160 or so and using that gap
between MBR and start of the first partition for environment it is not a
right thing to do. This way we are wasting some otherwise useable eMMC
storage space while still have plenty of unused space in 2 boot partitions.

If we put U-Boot in a boot partition it is logical to put its environment
in the same partition, isn't it? This is even more logical knowing the
fact it would save us some storage space for the OS filesystem...

But anyway, please hold off -- that patch won't apply because the alpine
email client "beautifies" text-only emails for some moronic reasons by
adding trailing whitespace to _SOME_ lines on mail _SEND_ thus screwing up
the patch. I will re-send that patch using git send-email that seems to
work correctly in a couple of hours. I will format it to follow official
rules and add proper CCs before re-sending.

Did you get that nand-bootupdate patch I re-sent yesterday with git
send-email? Did it work if you got it? It's been done against u-boot-imx.

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