Change in flashrom[master]: bitbang_spi: Add half-duplex optimizations

[Daniel Thompson (Code Review)]

Hello Paul Menzel, build bot (Jenkins), Nico Huber, Patrick Georgi,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/26947

to look at the new patch set (#3).

Change subject: bitbang_spi: Add half-duplex optimizations
......................................................................

bitbang_spi: Add half-duplex optimizations

Currently, the core of bitbang_spi is a full-duplex SPI loop but in
practice this code is only ever used half-duplex. Spliting this code
into two half duplex loops allows us to optimize performance by reducing
communications and/or CPU pipeline stalls.

The speed up varies depending on how much the overhead of
getting/setting pins dominates execution time. For a USB bit bang driver
running on a 7th generation Core i5, the time to probe drops from ~7.7
seconds to ~6.7 seconds when this patch is applied.

Change-Id: I33b9f363716f651146c09113bda5fffe53b16738
Signed-off-by: Daniel Thompson 
---
M bitbang_spi.c
1 file changed, 19 insertions(+), 5 deletions(-)

git pull ssh://review.coreboot.org:29418/flashrom refs/changes/47/26947/3