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/*
* This file is part of the coreboot project.
*
* Copyright 2018 Google LLC
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#include <console/console.h>
#include <delay.h>
#include <spi_bitbang.h>
/* Set to 1 to dump all SPI transfers to the UART. */
#define TRACE 0
/*
* In theory, this should work fine with 0 delay since the bus is fully clocked
* by the master and the slave just needs to follow clock transitions whenever
* they happen. We're not going to be "too fast" by bit-banging anyway. However,
* if something doesn't work right, try increasing this value to slow it down.
*/
#define HALF_CLOCK_US 0
int spi_bitbang_claim_bus(const struct spi_bitbang_ops *ops)
{
ops->set_cs(ops, 0);
return 0;
}
void spi_bitbang_release_bus(const struct spi_bitbang_ops *ops)
{
ops->set_cs(ops, 1);
}
/* Implements a CPOL=0, CPH=0, MSB first 8-bit controller. */
int spi_bitbang_xfer(const struct spi_bitbang_ops *ops, const void *dout,
size_t bytes_out, void *din, size_t bytes_in)
{
if (TRACE) {
if (bytes_in && bytes_out)
printk(BIOS_SPEW, "!");
else if (bytes_in)
printk(BIOS_SPEW, "<");
else if (bytes_out)
printk(BIOS_SPEW, ">");
}
while (bytes_out || bytes_in) {
int i;
uint8_t in_byte = 0, out_byte = 0;
if (bytes_out) {
out_byte = *(const uint8_t *)dout++;
bytes_out--;
if (TRACE)
printk(BIOS_SPEW, "%02x", out_byte);
}
for (i = 7; i >= 0; i--) {
ops->set_mosi(ops, !!(out_byte & (1 << i)));
if (HALF_CLOCK_US)
udelay(HALF_CLOCK_US);
ops->set_clk(ops, 1);
in_byte |= !!ops->get_miso(ops) << i;
if (HALF_CLOCK_US)
udelay(HALF_CLOCK_US);
ops->set_clk(ops, 0);
}
if (bytes_in) {
*(uint8_t *)din++ = in_byte;
bytes_in--;
if (TRACE)
printk(BIOS_SPEW, "%02x", in_byte);
}
}
if (TRACE)
printk(BIOS_SPEW, "\n");
return 0;
}
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