tree b88670c117c4b451366bb03fbe2229b05b56775f
parent 7e57f0493a661e57c5a2572a8818d35267482922
author Jason Wessel <jason.wessel@windriver.com> 1242658827 -0500
committer Anthony Liguori <aliguori@us.ibm.com> 1243007435 -0500

serial: fix lost character after sysrq

After creating an automated regression test to test the sysrq
responses while running a linux image in qemu, I found that the
simulated uart was eating the character right after the sysrq about
75% of the time.

The problem is that the qemu sets the LSR_DR (data ready) bit on a
serial break.  The automated tests can send a break and the sysrq
character quickly enough that the qemu serial fifo has a real
character available. When there is valid character in the fifo, it
gets consumed by the serial driver in the guest OS.

The real hardware also appears to set the LSR_DR but always appears to
have a null byte in this condition.  This patch changes the qemu
behavior to match the tested characteristics of a real 16550 chip.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>