[Cbe-oss-dev] spufs, ppu-gdb: ppu-gdb's info spu mailbox shows garbage

[Kazunori Asayama]

I found (maybe) unexpected behaviors in SPUFS and ppu-gdb regarding
displaying contents of mailbox queues as below:

1. the current implementation of read operation on wbox_info node is
   inconsistent with the spec in the man page.

   The read operation on "wbox_info" is defined in the man page as:

       The wbox_info file contains an array of four-byte mailbox
       messages, which have been sent to the SPU. With current CBEA
       machines, the array is four items in length, so up to 4 * 4 =
       16 bytes can be read from this file. If any mailbox queue entry
       is empty, then the bytes read at the corresponding location are
       undefined.

   However, only up to 4 * (# of valid entries) can be read in the
   current implementation of SPUFS, while 4 bytes can always be read
   on "mbox_info" and "ibox_info" regardless of number of valid
   entries and this behavior satisfies the spec:

       The mbox_info and ibox_info files each contain the four-byte
       mailbox message that has been written by the SPU. If no message
       has been written to these mailboxes, then contents of these
       files is unde- fined. The mbox_stat, ibox_stat and wbox_stat
       files contain the available message count.

   That is,

       man page:

           - mbox_info, ibox_info and wbox_info retun all entries of
             the queues.

       implementation:

           - wbox_info returns only valid entries.
       	   - mbox_info and ibox_info return all entries.

       	   It seems odd that there is such difference between the
       	   actual behaviors of wbox_info, mbox_info and ibox_info...

2. ppu-gdb's "info spu mailbox" command shows garbage when there are
   invalid entries in "ibox_info" and/or "mbox_info".

   The current "info spu mailbox" command implementation,
   i.e. info_spu_mailbox_command() in gdb/spu-tdep.c, shows all data
   returned by mbox_info, ibox_info and wbox_info.

   However, garbage can be displayed because mbox_info and ibox_info
   return invalid values when they are not full.

My question is "what is the intended behavior?" I guess that one of
following a. or b. is intended one:

    a. - mbox_info, ibox_info and wbox_info should return only valid
         entries; i.e. the man page is incorrect.

       - gdb should show the all data returned by mbox_info, ibox_info
         and wbox_info; i.e. the current implementation is correct.

    b. - mbox_info, ibox_info and wbox_info should return 4 * (queue's
         length) bytes regardless of number of valid entries; i.e. the
         man page is correct.

       - gdb should show only valid entries in the returned data by
         mbox_info, ibox_info and wbox_info by checking mbox_stat,
         ibox_stat and wbox_stat; i.e. the current implementation is
         incorrect.

Or any other one ?

--
(ASAYAMA Kazunori
  (asayama at sm.sony.co.jp))
t