s390/sclp: increase sclp console line length

s390/sclp: increase sclp console line length

Kernel and console/TTY messages written to the SCLP line mode console
are wrapped at 80 characters per line by the associated SCLP driver.
This makes long lines of output difficult to read, and requires editing
of wrapped lines copied from the output device.

Neither the firmware interface used to access the SCLP console, nor the
HMC "Operating System Messages" web interface that displays these
messages require such a length limit. Also other operating systems such
as z/VM do not impose similar limits on messages they emit to the same
console device.

This patch therefore increases the limit to 320 characters per line to
make SCLP line mode console output more readable. As a result 99% of
lines written during a typical boot will not be wrapped, compared to
about 50% wrapped lines at 80 characters per line. Another positive
side-effect of this change is that the HMC console interface is able to
keep more messages in its history buffer due to fewer line-breaks being
generated.

In a worst case scenario this means that a 4k console buffer is emitted
with the last ~400 bytes empty (320 text + 78 headers). This is more
than offset by the fact that each line that is not truncated saves 78
header bytes in the buffer. As a result the actual number of emitted
buffers should be about the same as with the 80 character limit.

This patch also removes the differentiation between line lengths of
SCLP line mode output on z/VM and non-z/VM systems. While the z/VM
hypervisor adds a prefix in front of each line ('xx: ' where xx is the
number of the CPU issuing the message), adjusting Linux line lengths did
not significantly increase readability of console output, and makes even
less of a difference with longer lines.

Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>