staging: most: dim2-hdm: initialize DBR memory of synchronous channels

In the time after a synchronous DIM2 channel is enabled and before the
first buffer travels this channel, the DIM2 macro is babbling random
random data to the network.

This patch initializes the internal DBR memory of the DIM2 that is used
to transfer the synchronous data.
Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/most/hdm-dim2/dim2_hal.c

@@ -135,6 +135,27 @@ static void free_dbr(int offs, int size)
 
 /* -------------------------------------------------------------------------- */
 
+static void dim2_clear_dbr(u16 addr, u16 size)
+{
+	enum { MADR_TB_BIT = 30, MADR_WNR_BIT = 31 };
+
+	u16 const end_addr = addr + size;
+	u32 const cmd = bit_mask(MADR_WNR_BIT) | bit_mask(MADR_TB_BIT);
+
+	dimcb_io_write(&g.dim2->MCTL, 0);   /* clear transfer complete */
+	dimcb_io_write(&g.dim2->MDAT0, 0);
+
+	for (; addr < end_addr; addr++) {
+		dimcb_io_write(&g.dim2->MADR, cmd | addr);
+
+		/* wait till transfer is completed */
+		while ((dimcb_io_read(&g.dim2->MCTL) & 1) != 1)
+			continue;
+
+		dimcb_io_write(&g.dim2->MCTL, 0);  /* clear transfer complete */
+	}
+}
+
 static u32 dim2_read_ctr(u32 ctr_addr, u16 mdat_idx)
 {
 	dimcb_io_write(&g.dim2->MADR, ctr_addr);
@@ -794,6 +815,7 @@ u8 dim_init_sync(struct dim_channel *ch, u8 is_tx, u16 ch_address,
 
 	sync_init(ch, ch_address / 2, bytes_per_frame);
 
+	dim2_clear_dbr(ch->dbr_addr, ch->dbr_size);
 	dim2_configure_channel(ch->addr, CAT_CT_VAL_SYNC, is_tx,
 			       ch->dbr_addr, ch->dbr_size, 0, true);