[media] iguanair: explain tx carrier setup

Just comments. No functional changes.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

diff --git a/drivers/media/rc/iguanair.c b/drivers/media/rc/iguanair.c
index fdae05c4f3775d7f54050c8776f0b882ac2fe630..99a3a5a509e6a00839c22490c7349643f238e31d 100644 (file)
--- a/drivers/media/rc/iguanair.c
+++ b/drivers/media/rc/iguanair.c
@@ -286,10 +286,10 @@ static int iguanair_receiver(struct iguanair *ir, bool enable)
 }
 
 /*
- * The iguana ir creates the carrier by busy spinning after each pulse or
- * space. This is counted in CPU cycles, with the CPU running at 24MHz. It is
+ * The iguanair creates the carrier by busy spinning after each half period.
+ * This is counted in CPU cycles, with the CPU running at 24MHz. It is
  * broken down into 7-cycles and 4-cyles delays, with a preference for
- * 4-cycle delays.
+ * 4-cycle delays, minus the overhead of the loop itself (cycle_overhead).
  */
 static int iguanair_set_tx_carrier(struct rc_dev *dev, uint32_t carrier)
 {
@@ -316,7 +316,14 @@ static int iguanair_set_tx_carrier(struct rc_dev *dev, uint32_t carrier)
                sevens = (4 - cycles) & 3;
                fours = (cycles - sevens * 7) / 4;
 
-               /* magic happens here */
+               /*
+                * The firmware interprets these values as a relative offset
+                * for a branch. Immediately following the branches, there
+                * 4 instructions of 7 cycles (2 bytes each) and 110
+                * instructions of 4 cycles (1 byte each). A relative branch
+                * of 0 will execute all of them, branch further for less
+                * cycle burning.
+                */
                ir->packet->busy7 = (4 - sevens) * 2;
                ir->packet->busy4 = 110 - fours;
        }