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>

2 files changed, 27 insertions, 16 deletions

diff --git a/bitbang_spi.c b/bitbang_spi.c
index edbc3e903..2c7a3f1c7 100644
--- a/bitbang_spi.c
+++ b/bitbang_spi.c
@@ -32,16 +32,6 @@ static void bitbang_spi_set_sck(const struct bitbang_spi_master * const master,
 	master->set_sck(val);
 }
 
-static void bitbang_spi_set_mosi(const struct bitbang_spi_master * const master, int val)
-{
-	master->set_mosi(val);
-}
-
-static int bitbang_spi_get_miso(const struct bitbang_spi_master * const master)
-{
-	return master->get_miso();
-}
-
 static void bitbang_spi_request_bus(const struct bitbang_spi_master * const master)
 {
 	if (master->request_bus)
@@ -54,6 +44,26 @@ static void bitbang_spi_release_bus(const struct bitbang_spi_master * const mast
 		master->release_bus();
 }
 
+static void bitbang_spi_set_sck_set_mosi(const struct bitbang_spi_master * const master, int sck, int mosi)
+{
+	if (master->set_sck_set_mosi) {
+		master->set_sck_set_mosi(sck, mosi);
+		return;
+	}
+
+	master->set_sck(sck);
+	master->set_mosi(mosi);
+}
+
+static int bitbang_spi_set_sck_get_miso(const struct bitbang_spi_master * const master, int sck)
+{
+	if (master->set_sck_get_miso)
+		return master->set_sck_get_miso(sck);
+
+	master->set_sck(sck);
+	return master->get_miso();
+}
+
 static int bitbang_spi_send_command(struct flashctx *flash,
 				    unsigned int writecnt, unsigned int readcnt,
 				    const unsigned char *writearr,
@@ -101,8 +111,7 @@ int register_spi_bitbang_master(const struct bitbang_spi_master *master)
 	/* Only mess with the bus if we're sure nobody else uses it. */
 	bitbang_spi_request_bus(master);
 	bitbang_spi_set_cs(master, 1);
-	bitbang_spi_set_sck(master, 0);
-	bitbang_spi_set_mosi(master, 0);
+	bitbang_spi_set_sck_set_mosi(master, 0, 0);
 	/* FIXME: Release SPI bus here and request it again for each command or
 	 * don't release it now and only release it on programmer shutdown?
 	 */
@@ -117,13 +126,11 @@ static uint8_t bitbang_spi_rw_byte(const struct bitbang_spi_master *master,
 	int i;
 
 	for (i = 7; i >= 0; i--) {
-		bitbang_spi_set_mosi(master, (val >> i) & 1);
+		bitbang_spi_set_sck_set_mosi(master, 0, (val >> i) & 1);
 		programmer_delay(master->half_period);
-		bitbang_spi_set_sck(master, 1);
 		ret <<= 1;
-		ret |= bitbang_spi_get_miso(master);
+		ret |= bitbang_spi_set_sck_get_miso(master, 1);
 		programmer_delay(master->half_period);
-		bitbang_spi_set_sck(master, 0);
 	}
 	return ret;
 }
@@ -147,6 +154,7 @@ static int bitbang_spi_send_command(struct flashctx *flash,
 	for (i = 0; i < readcnt; i++)
 		readarr[i] = bitbang_spi_rw_byte(master, 0);
 
+	bitbang_spi_set_sck(master, 0);
 	programmer_delay(master->half_period);
 	bitbang_spi_set_cs(master, 1);
 	programmer_delay(master->half_period);
diff --git a/programmer.h b/programmer.h
index ff81036d8..7e530b632 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;
 };