path: root/README
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authorHans de Goede <>2015-05-05 13:13:36 +0200
committerHans de Goede <>2015-05-19 18:37:30 +0200
commita8552c7c9b53d1d4f36b95f2c80812d8a7bb4fff (patch)
tree72406ed8d3ee56813c595d837ec69864e0ee8df3 /README
parentf9b08fbf11add614f1773c5378a9026cd3d5c75f (diff)
console: Fix pre-console flushing via cfb_console being very slow
On my A10 OlinuxIno Lime I noticed a huge (5+ seconds) delay coming from console_init_r. This turns out to be caused by the preconsole buffer flushing to the cfb_console. The Lime only has a 16 bit memory bus and that is already heavy used to scan out the 1920x1080 framebuffer. The problem is that print_pre_console_buffer() was printing the buffer once character at a time and the cfb_console code then ends up doing a cache-flush for touched display lines for each character. This commit fixes this by first building a 0 terminated buffer and then printing it in one puts() call, avoiding unnecessary cache flushes. This changes the time for the flush from 5+ seconds to not noticable. The downside of this approach is that the pre-console buffer needs to fit on the stack, this is not that much to ask since we are talking about plain text here. This commit also adjusts the sunxi CONFIG_PRE_CON_BUF_SZ to actually fit on the stack. Sunxi currently is the only user of the pre-console code so no other boards need to be adjusted. Signed-off-by: Hans de Goede <> Reviewed-by: Tom Rini <>
Diffstat (limited to 'README')
1 files changed, 3 insertions, 0 deletions
diff --git a/README b/README
index 1ea397a35c..2e81ccc37c 100644
--- a/README
+++ b/README
@@ -948,6 +948,9 @@ The following options need to be configured:
bytes are output before the console is initialised, the
earlier bytes are discarded.
+ Note that when printing the buffer a copy is made on the
+ stack so CONFIG_PRE_CON_BUF_SZ must fit on the stack.
'Sane' compilers will generate smaller code if
CONFIG_PRE_CON_BUF_SZ is a power of 2
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