[U-Boot] [RFC] fastboot: sparse image handling and sessionId

[Steve Rae]

Maxime,

I suspect that the issue fixed
  in commit c7529db    fastboot: sparse: fix block addressing for
don't care chunk type

complicated the assumptions which led to the implementation of the "sessionId"
  in commit 1f8690a    sparse: Implement several chunks flashing

    The fastboot client will split the sparse images into several chunks if the
    image that it tries to flash is bigger than what the device can handle.

    In such a case, the bootloader is supposed to retain the last offset to
    which it wrote to, so that it can resume the writes at the right offset
    when flashing the next chunk.

    Retain the last offset we used, and use the session ID to know if we need
    it or not.


Testing of this scenario has revealed that "fastboot flash" works as follows:

When the image to download is larger than the
    "target reported max download size of 40960000 bytes",
the fastboot client (running on the host) essentially performs
multiple, independent fastboot download/write steps.

As seen in the logs below, each download/write step:
(a) starts at the same address (the address of the first block of the
partition...)
(b) ends at the same address (start address plus number of blocks "written"...)
(c) and uses the CHUNK_TYPE_DONT_CARE 'chunk_sz' to manipulate the
addresses to achieve (a) and (b)

Here is an example of the first three fastboot download/writes for a
large image to "file-system":
- in the first, data is written to 0x24000-0x37848, then there is a
CHUNK_TYPE_DONT_CARE which "moves" the address pointer to 0x424000
- in the second, it starts with a CHUNK_TYPE_DONT_CARE which "moves"
the address from 0x24000 to 0x37848, then writes from 0x37848-0x4b098,
then there is a CHUNK_TYPE_DONT_CARE which "moves" the address pointer
to 0x424000
- in the third, it starts with a CHUNK_TYPE_DONT_CARE which "moves"
the address from 0x24000 to 0x4b098, then writes from 0x4b098-0x5e8e0,
then there is a CHUNK_TYPE_DONT_CARE which "moves" the address pointer
to 0x424000


Starting download of 40932412 bytes
..........................................................................
downloading of 40932412 bytes finished
Flashing sparse image at offset 147456
Flashing Sparse Image
- this is the starting                      address: 0x24000
++++ (writing to flash)
- this is the CHUNK_TYPE_DONT_CARE (before) address: 0x37848
- this is the CHUNK_TYPE_DONT_CARE (after)  address: 0x424000
- this is the ending                        address: 0x424000
........ wrote 4194304 blocks to 'file-system'

Starting download of 40954208 bytes
..........................................................................
downloading of 40954208 bytes finished
Flashing sparse image at offset 147456
Flashing Sparse Image
- this is the starting                      address: 0x24000
- this is the CHUNK_TYPE_DONT_CARE (before) address: 0x24000
- this is the CHUNK_TYPE_DONT_CARE (after)  address: 0x37848
++++ (writing to flash)
- this is the CHUNK_TYPE_DONT_CARE (before) address: 0x4b098
- this is the CHUNK_TYPE_DONT_CARE (after)  address: 0x424000
- this is the ending                        address: 0x424000
........ wrote 4194304 blocks to 'file-system'

Starting download of 40955896 bytes
..........................................................................
downloading of 40955896 bytes finished
Flashing sparse image at offset 147456
Flashing Sparse Image
- this is the starting                      address: 0x24000
- this is the CHUNK_TYPE_DONT_CARE (before) address: 0x24000
- this is the CHUNK_TYPE_DONT_CARE (after)  address: 0x4b098
++++ (writing to flash)
- this is the CHUNK_TYPE_DONT_CARE (before) address: 0x5e8e0
- this is the CHUNK_TYPE_DONT_CARE (after)  address: 0x424000
- this is the ending                        address: 0x424000
........ wrote 4194304 blocks to 'file-system'

[... snip ...]


Therefore, I think that the "sessonId" that is implemented in U-Boot
is actually incorrect. There is no need to keep track of the addresses
as each "fastboot flash" download/write step is completely
independent.
And I actually need to remove it in order to get this working again:

-       if (session_id > 0)
-               start = last_offset;
-       else
-               start = storage->start;
+       start = storage->start;


Additionally (unfortunately) as with the previous discussion that we
had about this code:

#ifdef CONFIG_FASTBOOT_FLASH_MMC_DEV
                        total_blocks += blkcnt;
#endif

the NAND implementation requires a method to process "blkcnt" to
ensure the blkcnt skips the bad blocks...


Please advise, Steve