1 files changed, 43 insertions, 0 deletions

diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index f17da50402a4..243d1a1d78b2 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -449,6 +449,48 @@ int i2c_recover_bus(struct i2c_adapter *adap);
 int i2c_generic_gpio_recovery(struct i2c_adapter *adap);
 int i2c_generic_scl_recovery(struct i2c_adapter *adap);
 
+/**
+ * struct i2c_adapter_quirks - describe flaws of an i2c adapter
+ * @flags: see I2C_AQ_* for possible flags and read below
+ * @max_num_msgs: maximum number of messages per transfer
+ * @max_write_len: maximum length of a write message
+ * @max_read_len: maximum length of a read message
+ * @max_comb_1st_msg_len: maximum length of the first msg in a combined message
+ * @max_comb_2nd_msg_len: maximum length of the second msg in a combined message
+ *
+ * Note about combined messages: Some I2C controllers can only send one message
+ * per transfer, plus something called combined message or write-then-read.
+ * This is (usually) a small write message followed by a read message and
+ * barely enough to access register based devices like EEPROMs. There is a flag
+ * to support this mode. It implies max_num_msg = 2 and does the length checks
+ * with max_comb_*_len because combined message mode usually has its own
+ * limitations. Because of HW implementations, some controllers can actually do
+ * write-then-anything or other variants. To support that, write-then-read has
+ * been broken out into smaller bits like write-first and read-second which can
+ * be combined as needed.
+ */
+
+struct i2c_adapter_quirks {
+        u64 flags;
+        int max_num_msgs;
+        u16 max_write_len;
+        u16 max_read_len;
+        u16 max_comb_1st_msg_len;
+        u16 max_comb_2nd_msg_len;
+};
+
+/* enforce max_num_msgs = 2 and use max_comb_*_len for length checks */
+#define I2C_AQ_COMB                     BIT(0)
+/* first combined message must be write */
+#define I2C_AQ_COMB_WRITE_FIRST         BIT(1)
+/* second combined message must be read */
+#define I2C_AQ_COMB_READ_SECOND         BIT(2)
+/* both combined messages must have the same target address */
+#define I2C_AQ_COMB_SAME_ADDR           BIT(3)
+/* convenience macro for typical write-then read case */
+#define I2C_AQ_COMB_WRITE_THEN_READ     (I2C_AQ_COMB | I2C_AQ_COMB_WRITE_FIRST | \
+                                         I2C_AQ_COMB_READ_SECOND | I2C_AQ_COMB_SAME_ADDR)
+
 /*
  * i2c_adapter is the structure used to identify a physical i2c bus along
  * with the access algorithms necessary to access it.
@@ -474,6 +516,7 @@ struct i2c_adapter {
         struct list_head userspace_clients;
 
         struct i2c_bus_recovery_info *bus_recovery_info;
+        const struct i2c_adapter_quirks *quirks;
 };
 #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)