bitbang.c

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/* SPDX-License-Identifier: GPL-2.0-only */
 
#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;
}