[coreboot-gerrit] Patch merged into coreboot/master: 2fe505b libpayload: console: Allow output drivers to print whole strings at once

[gerrit at coreboot.org]

the following patch was just integrated into master:
commit 2fe505bd9a4ff4e3e8bf081f254e0b71e41997be
Author: Julius Werner <jwerner at chromium.org>
Date:   Thu Apr 17 20:00:20 2014 -0700

    libpayload: console: Allow output drivers to print whole strings at once
    
    The console output driver framework in libpayload is currently built on
    the putchar primitive, meaning that every driver's function gets called
    one character at a time. This becomes an issue when we add drivers that
    could output multiple characters at a time, but have a high constant
    overhead per invocation (such as the planned GDB stub, which needs to
    wrap a special frame around output strings and wait for an
    acknowledgement from the server).
    
    This patch adds a new 'write' function pointer to the
    console_output_driver structure as an alternative to 'putchar'. Output
    drivers need to provide at least one of the two ('write' is preferred if
    available). The CBMEM console driver is ported as a proof of concept
    (since it's our most performace-critical driver and should in theory
    benefit the most from less function pointer invocations, although it's
    probably still negligible compared to the big sprawling mess that is
    printf()).
    
    Even with this fix, the problem remains that printf() was written with
    the putchar primitive in mind. Even though normal text already contains
    an optimization to allow multiple characters at a time, almost all
    formatting directives cause their output (including things like
    padding whitespace) to be putchar()ed one character at a time.
    Therefore, this patch reworks parts of the output code (especially
    number printing) to all but remove that inefficiency (directives still
    invoke an extra write() call, but at least not one per character). Since
    I'm touching printf() core code anyway, I also tried to salvage what I
    could from that weird, broken "return negative on error" code path (not
    that any of our current output drivers can trigger it anyway).
    
    A final consequence of this patch is that the responsibility to prepend
    line feeds with carriage returns is moved into the output driver
    implementations. Doing this only makes sense for drivers with explicit
    cursor position control (i.e. serial or video), and things like the
    CBMEM console that appears like a normal file to the system really have
    no business containing carriage returns (we don't want people to
    accidentally associate us with Windows, now, do we?).
    
    BUG=chrome-os-partner:18390
    TEST=Made sure video and CBMEM console still look good, tried printf()
    with as many weird edge-case strings as I could find and compared serial
    output as well as sprintf() return value.
    
    Original-Change-Id: Ie05ae489332a0103461620f5348774b6d4afd91a
    Original-Signed-off-by: Julius Werner <jwerner at chromium.org>
    Original-Reviewed-on: https://chromium-review.googlesource.com/196384
    Original-Reviewed-by: Hung-Te Lin <hungte at chromium.org>
    Original-Reviewed-by: David Hendricks <dhendrix at chromium.org>
    (cherry picked from commit ab1ef0c07736fe1aa3e0baaf02d258731e6856c0)
    Signed-off-by: Marc Jones <marc.jones at se-eng.com>
    
    Change-Id: I78f5aedf6d0c3665924995cdab691ee0162de404
    Reviewed-on: http://review.coreboot.org/7880
    Tested-by: build bot (Jenkins)
    Reviewed-by: Patrick Georgi <pgeorgi at google.com>


See http://review.coreboot.org/7880 for details.

-gerrit