lspcon_i2c_spi: Extract I2C bus parameter handling

Introduce the `i2c_open_from_programmer_params` function to avoid having
to duplicate parameter parsing code on all I2C programmers. This also
allows having the same programmer parameters on all I2C programmers.

Change-Id: I006b311c88feea37fe4b217f769b21ca1505def9
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/52830
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
diff --git a/i2c_helper_linux.c b/i2c_helper_linux.c
index 963c399..15f8f2a 100644
--- a/i2c_helper_linux.c
+++ b/i2c_helper_linux.c
@@ -27,6 +27,7 @@
 
 #include "flash.h"
 #include "i2c_helper.h"
+#include "programmer.h"
 
 /* Null characters are placeholders for bus number digits */
 #define I2C_DEV_PREFIX	"/dev/i2c-\0\0\0"
@@ -76,6 +77,52 @@
 	return i2c_open_path(dev, addr, force);
 }
 
+static int get_bus_number(char *bus_str)
+{
+	char *bus_suffix;
+	errno = 0;
+	int bus = (int)strtol(bus_str, &bus_suffix, 10);
+	if (errno != 0 || bus_str == bus_suffix) {
+		msg_perr("%s: Could not convert 'bus'.\n", __func__);
+		return -1;
+	}
+
+	if (strlen(bus_suffix) > 0) {
+		msg_perr("%s: Garbage following 'bus' value.\n", __func__);
+		return -1;
+	}
+
+	msg_pinfo("Using I2C bus %d.\n", bus);
+	return bus;
+}
+
+int i2c_open_from_programmer_params(uint16_t addr, int force)
+{
+	int fd = -1;
+
+	char *bus_str = extract_programmer_param("bus");
+	char *device_path = extract_programmer_param("devpath");
+
+	if (device_path != NULL && bus_str != NULL) {
+		msg_perr("%s: only one of bus and devpath may be specified\n", __func__);
+		goto out;
+	}
+	if (device_path == NULL && bus_str == NULL) {
+		msg_perr("%s: one of bus and devpath must be specified\n", __func__);
+		goto out;
+	}
+
+	if (device_path != NULL)
+		fd = i2c_open_path(device_path, addr, force);
+	else
+		fd = i2c_open(get_bus_number(bus_str), addr, force);
+
+out:
+	free(bus_str);
+	free(device_path);
+	return fd;
+}
+
 int i2c_read(int fd, uint16_t addr, i2c_buffer_t *buf)
 {
 	if (buf->len == 0)