[RFC PATCH] soundwire: bus: Add flag to mark DPN_BlockCtrl1 as readonly

[Srinivas Kandagatla <srinivas.kandagatla@linaro.org>]

According to SoundWire Specification Version 1.2.
"A Data Port number X (in the range 0-14) which supports only one
value of WordLength may implement the WordLength field in the
DPX_BlockCtrl1 Register as Read-Only, returning the fixed value of
WordLength in response to reads."

As WSA881x interfaces in PDM mode making the only field "WordLength"
in DPX_BlockCtrl1" fixed and read-only. Behaviour of writing to this
register on WSA881x soundwire slave with Qualcomm Soundwire Controller
is throwing up an error. Not sure how other controllers deal with
writing to readonly registers, but this patch provides a way to avoid
writes to DPN_BlockCtrl1 register by providing a ro_blockctrl1_reg
flag in struct sdw_port_runtime.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
---

I will send patch for WSA881x to include this change once this patch
is accepted.

 drivers/soundwire/bus.h    |  2 ++
 drivers/soundwire/stream.c | 17 ++++++++++-------
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
index 204204a26db8..791e8d14093e 100644
--- a/drivers/soundwire/bus.h
+++ b/drivers/soundwire/bus.h
@@ -79,6 +79,7 @@ int sdw_find_col_index(int col);
  * @num: Port number. For audio streams, valid port number ranges from
  * [1,14]
  * @ch_mask: Channel mask
+ * @ro_blockctrl1_reg: Read Only flag for DPN_BlockCtrl1 register
  * @transport_params: Transport parameters
  * @port_params: Port parameters
  * @port_node: List node for Master or Slave port_list
@@ -89,6 +90,7 @@ int sdw_find_col_index(int col);
 struct sdw_port_runtime {
 	int num;
 	int ch_mask;
+	bool ro_blockctrl1_reg;
 	struct sdw_transport_params transport_params;
 	struct sdw_port_params port_params;
 	struct list_head port_node;
diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c
index 00348d1fc606..4491643aeb4a 100644
--- a/drivers/soundwire/stream.c
+++ b/drivers/soundwire/stream.c
@@ -167,13 +167,15 @@ static int sdw_program_slave_port_params(struct sdw_bus *bus,
 		return ret;
 	}
 
-	/* Program DPN_BlockCtrl1 register */
-	ret = sdw_write(s_rt->slave, addr2, (p_params->bps - 1));
-	if (ret < 0) {
-		dev_err(&s_rt->slave->dev,
-			"DPN_BlockCtrl1 register write failed for port %d\n",
-			t_params->port_num);
-		return ret;
+	if (!p_rt->ro_blockctrl1_reg) {
+		/* Program DPN_BlockCtrl1 register */
+		ret = sdw_write(s_rt->slave, addr2, (p_params->bps - 1));
+		if (ret < 0) {
+			dev_err(&s_rt->slave->dev,
+				"DPN_BlockCtrl1 register write failed for port %d\n",
+				t_params->port_num);
+			return ret;
+		}
 	}
 
 	/* Program DPN_SampleCtrl1 register */
@@ -1195,6 +1197,7 @@ static struct sdw_port_runtime
 
 	p_rt->ch_mask = port_config[port_index].ch_mask;
 	p_rt->num = port_config[port_index].num;
+	p_rt->ro_blockctrl1_reg = port_config[port_index].ro_blockctrl1_reg;
 
 	return p_rt;
 }
-- 
2.21.0