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  1. 08 1月, 2014 1 次提交
  3. 18 12月, 2013 1 次提交
  5. 17 12月, 2013 1 次提交
  7. 09 12月, 2013 2 次提交
  9. 04 10月, 2013 1 次提交
    • T
      serial: 8250_dw: Improve unwritable LCR workaround · c49436b6
      由 Tim Kryger 提交于 
      When configured with UART_16550_COMPATIBLE=NO or in versions prior to
the introduction of this option, the Designware UART will ignore writes
to the LCR if the UART is busy.  The current workaround saves a copy of
the last written LCR and re-writes it in the ISR for a special interrupt
that is raised when a write was ignored.

Unfortunately, interrupts are typically disabled prior to performing a
sequence of register writes that include the LCR so the point at which
the retry occurs is too late.  An example is serial8250_do_set_termios()
where an ignored LCR write results in the baud divisor not being set and
instead a garbage character is sent out the transmitter.

Furthermore, since serial_port_out() offers no way to indicate failure,
a serious effort must be made to ensure that the LCR is actually updated
before returning back to the caller.  This is difficult, however, as a
UART that was busy during the first attempt is likely to still be busy
when a subsequent attempt is made unless some extra action is taken.

This updated workaround reads back the LCR after each write to confirm
that the new value was accepted by the hardware.  Should the hardware
ignore a write, the TX/RX FIFOs are cleared and the receive buffer read
before attempting to rewrite the LCR out of the hope that doing so will
force the UART into an idle state.  While this may seem unnecessarily
aggressive, writes to the LCR are used to change the baud rate, parity,
stop bit, or data length so the data that may be lost is likely not
important.  Admittedly, this is far from ideal but it seems to be the
best that can be done given the hardware limitations.

Lastly, the revised workaround doesn't touch the LCR in the ISR, so it
avoids the possibility of a "serial8250: too much work for irq" lock up.
This problem is rare in real situations but can be reproduced easily by
wiring up two UARTs and running the following commands.

  # stty -F /dev/ttyS1 echo
  # stty -F /dev/ttyS2 echo
  # cat /dev/ttyS1 &
  [1] 375
  # echo asdf > /dev/ttyS1
  asdf

  [   27.700000] serial8250: too much work for irq96
  [   27.700000] serial8250: too much work for irq96
  [   27.710000] serial8250: too much work for irq96
  [   27.710000] serial8250: too much work for irq96
  [   27.720000] serial8250: too much work for irq96
  [   27.720000] serial8250: too much work for irq96
  [   27.730000] serial8250: too much work for irq96
  [   27.730000] serial8250: too much work for irq96
  [   27.740000] serial8250: too much work for irq96
Signed-off-by: NTim Kryger <tim.kryger@linaro.org>
Reviewed-by: NMatt Porter <matt.porter@linaro.org>
Reviewed-by: NMarkus Mayer <markus.mayer@linaro.org>
Reviewed-by: NHeikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      c49436b6
  11. 28 9月, 2013 1 次提交
  13. 27 9月, 2013 2 次提交
  15. 20 8月, 2013 1 次提交
    • T
      serial: 8250_dw: Report CTS asserted for auto flow · 33acbb82
      由 Tim Kryger 提交于 
      When a serial port is configured for RTS/CTS flow control, serial core
will disable the transmitter if it observes CTS is de-asserted. This is
perfectly reasonable and appropriate when the UART lacks the ability to
automatically perform CTS flow control.

However, if the UART hardware can manage flow control automatically, it
is important that software not get involved.  When the DesignWare UART
enables 16C750 style auto-RTS/CTS it stops generating interrupts for
changes in CTS state so software mostly stays out of the way.  However,
it does report the true state of CTS in the MSR so software may notice
it is de-asserted and respond by improperly disabling the transmitter.
Once this happens the transmitter will be blocked forever.

To avoid this situation, we simply lie to the 8250 and serial core by
reporting that CTS is asserted whenever auto-RTS/CTS mode is enabled.
Signed-off-by: NTim Kryger <tim.kryger@linaro.org>
Reviewed-by: NMatt Porter <matt.porter@linaro.org>
Reviewed-by: NMarkus Mayer <markus.mayer@linaro.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      33acbb82
  17. 01 7月, 2013 1 次提交
  19. 22 5月, 2013 1 次提交
  21. 21 5月, 2013 1 次提交
  23. 13 4月, 2013 1 次提交
  25. 12 4月, 2013 5 次提交
  27. 29 3月, 2013 1 次提交
  29. 16 1月, 2013 9 次提交
  31. 22 11月, 2012 3 次提交
  33. 25 10月, 2012 1 次提交
  35. 18 7月, 2012 1 次提交
  37. 13 7月, 2012 1 次提交
  39. 25 1月, 2012 1 次提交
  41. 30 11月, 2011 1 次提交
  43. 27 8月, 2011 1 次提交
  45. 25 8月, 2011 1 次提交
  47. 24 8月, 2011 1 次提交