bitbang_spi: Add functions to optimize xfers

On systems where the overhead of getting/setting pins is much greater
than the half period (for example, USB bit banging) it significantly
boosts performance if we can bang more than one bit at the same time.
Add support for setting sck at the same time as mosi or miso activity.

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 ~9.2
seconds to ~7.7 seconds when set_clk_set_mosi() is implemented.

Change-Id: Ic3430a9df34844cdfa82e109456be788eaa1789a
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-on: https://review.coreboot.org/26946
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Idwer Vollering <vidwer@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>

1 files changed, 3 insertions, 0 deletions

diff --git a/programmer.h b/programmer.h
index ff81036d..7e530b63 100644
--- a/programmer.h
+++ b/programmer.h
@@ -184,6 +184,9 @@ struct bitbang_spi_master {
 	int (*get_miso) (void);
 	void (*request_bus) (void);
 	void (*release_bus) (void);
+	/* optional functions to optimize xfers */
+	void (*set_sck_set_mosi) (int sck, int mosi);
+	int (*set_sck_get_miso) (int sck);
 	/* Length of half a clock period in usecs. */
 	unsigned int half_period;
 };