Change in flashrom[master]: bitbang_spi: Add functions to optimize xfers

[Nico Huber (Code Review)]

Nico Huber has submitted this change and it was merged. ( https://review.coreboot.org/26946 )

Change subject: bitbang_spi: Add functions to optimize xfers
......................................................................

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 
Reviewed-on: https://review.coreboot.org/26946
Tested-by: build bot (Jenkins) 
Reviewed-by: Patrick Georgi 
Reviewed-by: Idwer Vollering 
Reviewed-by: Nico Huber 
---
M bitbang_spi.c
M programmer.h
2 files changed, 27 insertions(+), 16 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Patrick Georgi: Looks good to me, but someone else must approve
  Idwer Vollering: Looks good to me, but someone else must approve
  Nico Huber: Looks good to me, approved

diff --git a/bitbang_spi.c b/bitbang_spi.c
index edbc3e9..2c7a3f1 100644
--- a/bitbang_spi.c
+++ b/bitbang_spi.c
@@ -32,16 +32,6 @@
    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 @@
    	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 @@
    /* 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 @@
    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 @@
    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 ff81036..7e530b6 100644
--- a/programmer.h
+++ b/programmer.h
@@ -184,6 +184,9 @@
    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;
 };