ddr: altera: Internal rw_mgr_mem_calibrate_vfifo() cleanup part 1

This patch just adds an expanded documentation header to the
aforementioned function. This is needed to make it easier to
match the purpose of this function with the documentation.

No functional change.

Signed-off-by: Marek Vasut <marex@denx.de>

drivers/ddr/altera/sequencer.c

@@ -2186,11 +2186,19 @@ static uint32_t rw_mgr_mem_calibrate_vfifo_center(uint32_t rank_bgn,
 	return (dq_margin >= 0) && (dqs_margin >= 0);
 }
 
-/*
- * calibrate the read valid prediction FIFO.
+/**
+ * rw_mgr_mem_calibrate_vfifo() - Calibrate the read valid prediction FIFO
+ * @rw_group:		Read/Write Group
+ * @test_bgn:		Rank at which the test begins
  *
- *  - read valid prediction will consist of finding a good DQS enable phase,
- * DQS enable delay, DQS input phase, and DQS input delay.
+ * Stage 1: Calibrate the read valid prediction FIFO.
+ *
+ * This function implements UniPHY calibration Stage 1, as explained in
+ * detail in Altera EMI_RM 2015.05.04 , "UniPHY Calibration Stages".
+ *
+ * - read valid prediction will consist of finding:
+ *   - DQS enable phase and DQS enable delay (DQS Enable Calibration)
+ *   - DQS input phase  and DQS input delay (DQ/DQS Centering)
  *  - we also do a per-bit deskew on the DQ lines.
  */
 static uint32_t rw_mgr_mem_calibrate_vfifo(uint32_t read_group,