[Qemu-devel] [PATCH v1 00/11] Cadence UART cleanups and Tx path fixes

[Peter Crosthwaite]

When using QEMU in some terminal environments, char back-ends for serial
devices can return EAGAIN for non trivial periods. This coupled with use
of qemu_chr_fe_write_all() is a leading cause of:

main-loop: WARNING: I/O thread spun for 1000 iterations

This series fixes this for cadence_uart by replacing the open loop
tx-write logic with a proper closed-loop that is responsive to the
back-end short return.

Various trivial cleanups are at the front of the series. Last patch is
the main event.

There is also a major performance increase with removal of the tx timer
logic (P7).

As a test, I've been using QEMU in a terminal over trans-pacific SSH.
Before this series:

$ time ./qemu-build/arm-softmmu/qemu-system-arm -M xilinx-zynq-a9 ...
main-loop: WARNING: I/O thread spun for 1000 iterations
Booting Linux on physical CPU 0x0
...
PetaLinux v2013.04 (Yocto 1.3) zynq ttyPS0

zynq login: QEMU: Terminated

real    2m26.908s
user    1m41.430s
sys     1m7.116s

And after:

$ time ./qemu-build/arm-softmmu/qemu-system-arm -M xilinx-zynq-a9 ...
Booting Linux on physical CPU 0x0
...
PetaLinux v2013.04 (Yocto 1.3) zynq ttyPS0

zynq login: QEMU: Terminated

real    0m16.149s
user    0m10.357s
sys     0m0.164s


Peter Crosthwaite (11):
  char/cadence_uart: Mark struct fields as public/private
  char/cadence_uart: Add missing uart_update_state
  char/cadence_uart: Fix reset.
  char/cadence_uart: s/r_fifo/rx_fifo
  char/cadence_uart: Simplify status generation
  char/cadence_uart: Define Missing SR/ISR fields
  char/cadence_uart: Remove TX timer & add TX FIFO state
  char/cadence_uart: Fix can_receive logic
  char/cadence_uart: Use the TX fifo for transmission
  char/cadence_uart: Delete redundant rx rst logic
  char/cadence_uart: Implement Tx flow control

 hw/char/cadence_uart.c | 153 ++++++++++++++++++++++++++++---------------------
 1 file changed, 87 insertions(+), 66 deletions(-)

-- 
1.8.5.1