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bitbang_spi: Add half-duplex optimizations

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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 <daniel.thompson@linaro.org>
Reviewed-on: https://review.coreboot.org/26947
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
This commit is contained in:
Daniel Thompson 2018-06-05 09:55:20 +01:00 committed by Nico Huber
parent b623f403a0
commit 455a6fc86e
1 changed files with 19 additions and 5 deletions
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24
bitbang_spi.c
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@ -119,14 +119,16 @@ int register_spi_bitbang_master(const struct bitbang_spi_master *master)
return 0;
}
static uint8_t bitbang_spi_rw_byte(const struct bitbang_spi_master *master,
uint8_t val)
static uint8_t bitbang_spi_read_byte(const struct bitbang_spi_master *master)
{
uint8_t ret = 0;
int i;
for (i = 7; i >= 0; i--) {
bitbang_spi_set_sck_set_mosi(master, 0, (val >> i) & 1);
if (i == 0)
bitbang_spi_set_sck_set_mosi(master, 0, 0);
else
bitbang_spi_set_sck(master, 0);
programmer_delay(master->half_period);
ret <<= 1;
ret |= bitbang_spi_set_sck_get_miso(master, 1);
@ -135,6 +137,18 @@ static uint8_t bitbang_spi_rw_byte(const struct bitbang_spi_master *master,
return ret;
}
static void bitbang_spi_write_byte(const struct bitbang_spi_master *master, uint8_t val)
{
int i;
for (i = 7; i >= 0; i--) {
bitbang_spi_set_sck_set_mosi(master, 0, (val >> i) & 1);
programmer_delay(master->half_period);
bitbang_spi_set_sck(master, 1);
programmer_delay(master->half_period);
}
}
static int bitbang_spi_send_command(struct flashctx *flash,
unsigned int writecnt, unsigned int readcnt,
const unsigned char *writearr,
@ -150,9 +164,9 @@ static int bitbang_spi_send_command(struct flashctx *flash,
bitbang_spi_request_bus(master);
bitbang_spi_set_cs(master, 0);
for (i = 0; i < writecnt; i++)
bitbang_spi_rw_byte(master, writearr[i]);
bitbang_spi_write_byte(master, writearr[i]);
for (i = 0; i < readcnt; i++)
readarr[i] = bitbang_spi_rw_byte(master, 0);
readarr[i] = bitbang_spi_read_byte(master);
bitbang_spi_set_sck(master, 0);
programmer_delay(master->half_period);