i2c_controller: Add i2c_read_sized_block function

Currently there is `i2c_read_string` that reads data in the form
`[Length] [byte 0] ... [byte Length-1]`. However this function only
reads null terminated strings. This commit adds `i2c_read_sized_block`
to support reading a general block of data with a length. This commit
also re-implements `i2c_read_string` in terms of `i2c_read_sized_block`
This changes the behavior of `i2c_read_string` to produce an empty
string on failure.

BUG=b:228589840
TEST=Verified that battery strings are read properly, used i2ctrace to
verify that `i2c_read_sized_block` reads the correct number of bytes
BRANCH=none

Signed-off-by: Robert Zieba <robertzieba@google.com>
Change-Id: Id4aaf727048329776311eec5d392aafbd1eef2b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3605884
Reviewed-by: Diana Z <dzigterman@chromium.org>
Commit-Queue: Diana Z <dzigterman@chromium.org>

2 files changed, 37 insertions, 7 deletions

diff --git a/common/i2c_controller.c b/common/i2c_controller.c
index 5064deb073..f29b40b251 100644
--- a/common/i2c_controller.c
+++ b/common/i2c_controller.c
@@ -765,13 +765,16 @@ int i2c_write_offset16_block(const int port,
 	return rv;
 }
 
-int i2c_read_string(const int port,
-		    const uint16_t addr_flags,
-		    int offset, uint8_t *data, int len)
+int i2c_read_sized_block(const int port,
+			 const uint16_t addr_flags,
+			 int offset, uint8_t *data, int max_len, int *read_len)
 {
 	int i, rv;
 	uint8_t reg, block_length;
 
+	if (max_len == 0)
+		return EC_ERROR_INVAL;
+
 	if (!IS_ENABLED(CONFIG_SMBUS_PEC) && I2C_USE_PEC(addr_flags))
 		return EC_ERROR_UNIMPLEMENTED;
 
@@ -791,8 +794,8 @@ int i2c_read_string(const int port,
 		if (rv)
 			continue;
 
-		if (len && block_length > (len - 1))
-			data_length = len - 1;
+		if (max_len && block_length > max_len)
+			data_length = max_len;
 		else
 			data_length = block_length;
 
@@ -805,7 +808,6 @@ int i2c_read_string(const int port,
 
 			rv = i2c_xfer_unlocked(port, addr_flags,
 					       0, 0, data, data_length, 0);
-			data[data_length] = 0;
 			if (rv)
 				continue;
 
@@ -839,12 +841,12 @@ int i2c_read_string(const int port,
 			rv = i2c_xfer_unlocked(port, addr_flags,
 					       0, 0, data, data_length,
 					       I2C_XFER_STOP);
-			data[data_length] = 0;
 			if (rv)
 				continue;
 		}
 
 		/* execution reaches here implies rv=0, so we can exit now */
+		*read_len = data_length;
 		break;
 	}
 
@@ -852,6 +854,22 @@ int i2c_read_string(const int port,
 	return rv;
 }
 
+int i2c_read_string(const int port,
+		    const uint16_t addr_flags,
+		    int offset, uint8_t *data, int len)
+{
+	int read_len = 0;
+	int rv = 0;
+
+	if (len == 0)
+		return EC_ERROR_INVAL;
+
+	rv = i2c_read_sized_block(port, addr_flags, offset, data, len - 1,
+				      &read_len);
+	data[read_len] = 0;
+	return rv;
+}
+
 int i2c_read_block(const int port, const uint16_t addr_flags, int offset,
 		   uint8_t *data, int len)
 {
diff --git a/include/i2c.h b/include/i2c.h
index 86c6e24e85..3ae1f60d97 100644
--- a/include/i2c.h
+++ b/include/i2c.h
@@ -442,6 +442,18 @@ int i2c_is_busy(int port);
 int i2c_unwedge(int port);
 
 /**
+ * Read read using  smbus read block protocol.
+ * Read bytestream from <addr_flags>:<offset> with format:
+ *     [length_N] [byte_0] [byte_1] ... [byte_N]
+ *
+ * <len>      : the max length of receiving buffer
+ * <len> == 0 : buffer size > 255
+ */
+int i2c_read_sized_block(const int port,
+			 const uint16_t addr_flags,
+			 int offset, uint8_t *data, int max_len, int *read_len);
+
+/**
  * Read ascii string using smbus read block protocol.
  * Read bytestream from <addr_flags>:<offset> with format:
  *     [length_N] [byte_0] [byte_1] ... [byte_N-1]