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  1. 16 12月, 2014 2 次提交
    • P
      serial: update LSR on enabling/disabling FIFOs · 023c3a97
      由 Paolo Bonzini 提交于 
      When the transmit FIFO is emptied or enabled, the transmitter
hold register is empty.  When it is disabled, it is also emptied and
in addition the previous contents of the transmitter hold register
are discarded.  In either case, the THRE bit in LSR must be set and
THRI raised.

When the receive FIFO is emptied or enabled, the data ready and break
bits must be cleared in LSR.  Likewise when the receive FIFO is disabled.
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
      023c3a97
    • P
      serial: clean up THRE/TEMT handling · 0d931d70
      由 Paolo Bonzini 提交于 
      - assert TEMT is cleared before sending a character; we'll get one from
TSR if tsr_retry > 0, from the FIFO or THR otherwise

- assert THRE cleared and FIFO not empty (if enabled) before fetching a
character to send.  This effectively reverts dffacd46, but the check
makes no sense and commit f702e62a (serial: change retry logic to avoid
concurrency, 2014-07-11) must have made it unnecessary.  The commit
message for f702e62a talks about multiple calls to qemu_chr_fe_add_watch
triggering s->tsr_retry >= MAX_XMIT_RETRY, but other failures were
possible.  For example, if you have multiple calls, the subsequent ones
will see s->tsr_retry == 0 and will find THRE and/or TEMT on entry.

- for clarity, raise THRI immediately after the code sets THRE

- check THRE to see if another character has to be sent.  This makes
the assertions more obvious and also means TEMT has to be set as soon as
the loop ends.  It makes the loop send both TSR and THR if flow-control
happens in non-FIFO mode.  Previously, THR would be lost.

- clear TEMT together with THRE even in the non-FIFO case

The last two items are bugfixes, but they were just found by inspection
and do not squash known bugs.
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
      0d931d70
  3. 15 12月, 2014 38 次提交