lspcon_i2c_spi: support a devpath option

Some callers may find it easier to provide the path to an I2C device
at which to communicate with the device, rather than specify the bus
number- doing so might involve trying to parse a path to extract the
number only for flashrom to do the reverse, which is error-prone and
unnecessary.

This change adds support for a `devpath` option, continuing to
allow `bus` and requiring only one of them be specified.

TEST=Verified --flash-size outputs correct values with both
     devpath=/dev/i2c-7 and bus=7, as well as noting that one is
     required if neither is specified and only one may be specified
     if both are given.

Signed-off-by: Peter Marheine <pmarheine@chromium.org>
Change-Id: Id2adf8a307b9205ce5e5804a6c3e22f19d0c34c9
Reviewed-on: https://review.coreboot.org/c/flashrom/+/51967
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

3 files changed, 80 insertions, 52 deletions

diff --git a/i2c_helper.h b/i2c_helper.h
index 599e08bbd..cab2ce6f3 100644
--- a/i2c_helper.h
+++ b/i2c_helper.h
@@ -72,6 +72,14 @@ static inline int i2c_buffer_t_fill(i2c_buffer_t *i2c_buf, void *buf, uint16_t l
 int i2c_open(int bus, uint16_t addr, int force);
 
 /**
+ * i2c_open_path: open an I2C device by device path
+ *
+ * This function behaves the same as i2c_open, but takes a filesystem
+ * path (assumed to be an I2C device file) instead of a bus number.
+ */
+int i2c_open_path(const char *path, uint16_t addr, int force);
+
+/**
  * i2c_close - closes the file descriptor returned by i2c_open
  *
  * @fd:	file descriptor to be closed.
diff --git a/i2c_helper_linux.c b/i2c_helper_linux.c
index 9383c8572..774450527 100644
--- a/i2c_helper_linux.c
+++ b/i2c_helper_linux.c
@@ -37,14 +37,31 @@ int i2c_close(int fd)
 	return fd == -1 ? 0 : close(fd);
 }
 
+int i2c_open_path(const char *path, uint16_t addr, int force)
+{
+	int fd = open(path, O_RDWR);
+	if (fd < 0) {
+		msg_perr("Unable to open I2C device %s: %s.\n", path, strerror(errno));
+		return fd;
+	}
+
+	int request = force ? I2C_SLAVE_FORCE : I2C_SLAVE;
+	int ret = ioctl(fd, request, addr);
+	if (ret < 0) {
+		msg_perr("Unable to set I2C slave address to 0x%02x: %s.\n", addr, strerror(errno));
+		i2c_close(fd);
+                return ret;
+	}
+
+	return fd;
+}
+
+
 int i2c_open(int bus, uint16_t addr, int force)
 {
 	char dev[sizeof(I2C_DEV_PREFIX)] = {0};
 
 	int ret = -1;
-	int fd = -1;
-
-	int request = force ? I2C_SLAVE_FORCE : I2C_SLAVE;
 
 	if (bus < 0 || bus > I2C_MAX_BUS) {
 		msg_perr("Invalid I2C bus %d.\n", bus);
@@ -57,20 +74,7 @@ int i2c_open(int bus, uint16_t addr, int force)
 		return ret;
 	}
 
-	fd = open(dev, O_RDWR);
-	if (fd < 0) {
-		msg_perr("Unable to open I2C device %s: %s.\n", dev, strerror(errno));
-		return fd;
-	}
-
-	ret = ioctl(fd, request, addr);
-	if (ret < 0) {
-		msg_perr("Unable to set I2C slave address to 0x%02x: %s.\n", addr, strerror(errno));
-		i2c_close(fd);
-		return ret;
-	}
-
-	return fd;
+	return i2c_open_path(dev, addr, force);
 }
 
 int i2c_read(int fd, uint16_t addr, i2c_buffer_t *buf)
diff --git a/lspcon_i2c_spi.c b/lspcon_i2c_spi.c
index 7599db6b0..b79e7f7b4 100644
--- a/lspcon_i2c_spi.c
+++ b/lspcon_i2c_spi.c
@@ -434,56 +434,72 @@ static int lspcon_i2c_spi_shutdown(void *data)
 }
 
 /* TODO: remove this out of the specific SPI master implementation. */
-static int get_bus(void)
+static int get_bus_number(void)
 {
 	char *bus_str = extract_programmer_param("bus");
-        int ret = SPI_GENERIC_ERROR;
-	if (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__);
-			goto get_bus_done;
-		}
-
-		if (bus < 0 || bus > 255) {
-			msg_perr("%s: Value for 'bus' is out of range(0-255).\n",
-                                 __func__);
-			goto get_bus_done;
-		}
-
-		if (strlen(bus_suffix) > 0) {
-			msg_perr("%s: Garbage following 'bus' value.\n",
-                                 __func__);
-			goto get_bus_done;
-		}
-
-		msg_pinfo("Using i2c bus %i.\n", bus);
-		ret = bus;
+	/* Return INVALID_ADDRESS if bus value was given but invalid, and GENERIC_ERROR
+	 * if no value was provided. */
+        int ret = SPI_INVALID_ADDRESS;
+
+        if (bus_str == NULL)
+        	return SPI_GENERIC_ERROR;
+
+	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__);
+		goto get_bus_done;
+	}
+
+	if (bus < 0 || bus > 255) {
+		msg_perr("%s: Value for 'bus' is out of range(0-255).\n", __func__);
 		goto get_bus_done;
-	} else {
-		msg_perr("%s: Bus number not specified.\n", __func__);
 	}
-get_bus_done:
-	if (bus_str)
-		free(bus_str);
 
+	if (strlen(bus_suffix) > 0) {
+		msg_perr("%s: Garbage following 'bus' value.\n", __func__);
+		goto get_bus_done;
+	}
+
+	msg_pinfo("Using i2c bus %i.\n", bus);
+	ret = bus;
+
+get_bus_done:
+	free(bus_str);
 	return ret;
 }
 
 int lspcon_i2c_spi_init(void)
 {
-	int lspcon_i2c_spi_bus = get_bus();
-	if (lspcon_i2c_spi_bus < 0)
+	int fd = -1;
+	int bus_number = get_bus_number();
+	if (bus_number == SPI_INVALID_ADDRESS) {
+		/* Bus was specified but unusable, bail out immediately */
 		return SPI_GENERIC_ERROR;
+	}
+	char *device_path = extract_programmer_param("devpath");
+
+	if (device_path != NULL && bus_number >= 0) {
+		msg_perr("%s: only one of bus and devpath may be specified\n", __func__);
+		free(device_path);
+		return SPI_GENERIC_ERROR;
+	} else if (device_path == NULL && bus_number < 0) {
+		msg_perr("%s: one of bus and devpath must be specified\n", __func__);
+		return SPI_GENERIC_ERROR;
+	}
+
+	if (device_path != NULL) {
+		fd = i2c_open_path(device_path, REGISTER_ADDRESS, 0);
+		free(device_path);
+	} else {
+		fd = i2c_open(bus_number, REGISTER_ADDRESS, 0);
+	}
 
-	int ret = 0;
-	int fd = i2c_open(lspcon_i2c_spi_bus, REGISTER_ADDRESS, 0);
 	if (fd < 0)
 		return fd;
 
-	ret |= lspcon_i2c_spi_reset_mpu_stop(fd);
+	int ret = lspcon_i2c_spi_reset_mpu_stop(fd);
 	if (ret) {
 		msg_perr("%s: call to reset_mpu_stop failed.\n", __func__);
 		return ret;