Comment 7 for bug 1892290

Similar bug: https://bugzilla.redhat.com/show_bug.cgi?id=1869987
I've tried boot by cmdline, looks the same issue.
grub> linux vmlinuz-5.4.0-47-generic
grub> echo $?
0
grub> initrd initrd.img-5.4.0-47-generic
error: timeout reading `initrd.img-5.4.0-47-generic'.
grub> echo $?
28

It looks like it is caused by Commit 781b3e5efc3 (tftp: Do not use priority queue) .
And bellow upstream commit can fix it.

commit a6838bbc6726ad624bd2b94991f690b8e9d23c69
Author: Javier Martinez Canillas <email address hidden>
Date: Thu Sep 10 17:17:57 2020 +0200

    tftp: Roll-over block counter to prevent data packets timeouts

    Commit 781b3e5efc3 (tftp: Do not use priority queue) caused a regression
    when fetching files over TFTP whose size is bigger than 65535 * block size.

      grub> linux /images/pxeboot/vmlinuz
      grub> echo $?
      0
      grub> initrd /images/pxeboot/initrd.img
      error: timeout reading '/images/pxeboot/initrd.img'.
      grub> echo $?
      28

    It is caused by the block number counter being a 16-bit field, which leads
    to a maximum file size of ((1 << 16) - 1) * block size. Because GRUB sets
    the block size to 1024 octets (by using the TFTP Blocksize Option from RFC
    2348 [0]), the maximum file size that can be transferred is 67107840 bytes.

    The TFTP PROTOCOL (REVISION 2) RFC 1350 [1] does not mention what a client
    should do when a file size is bigger than the maximum, but most TFTP hosts
    support the block number counter to be rolled over. That is, acking a data
    packet with a block number of 0 is taken as if the 65356th block was acked.

    It was working before because the block counter roll-over was happening due
    an overflow. But that got fixed by the mentioned commit, which led to the
    regression when attempting to fetch files larger than the maximum size.

    To allow TFTP file transfers of unlimited size again, re-introduce a block
    counter roll-over so the data packets are acked preventing the timeouts.

    [0]: https://tools.ietf.org/html/rfc2348
    [1]: https://tools.ietf.org/html/rfc1350

    Fixes: 781b3e5efc3 (tftp: Do not use priority queue)

    Suggested-by: Peter Jones <email address hidden>
    Signed-off-by: Javier Martinez Canillas <email address hidden>
    Reviewed-by: Daniel Kiper <email address hidden>