1 files changed, 84 insertions, 0 deletions
diff --git a/src/drivers/spi/bitbang.c b/src/drivers/spi/bitbang.c
new file mode 100644
index 0000000000..d858345859
--- /dev/null
+++ b/src/drivers/spi/bitbang.c
@@ -0,0 +1,84 @@
+/*
+ * 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;
+}