[PATCH 1/3] soundwire: allow drivers to check whether the peripheral is present

[Bard Liao <yung-chuan.liao@linux.intel.com>]

A ghost peripheral may be listed in the ACPI table and we want to skip
it. Add enumeration_complete and is_present in struct sdw_bus{} allow
the driver to wait and check whether a peripheral is present.

Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
---
 drivers/soundwire/bus.c       | 7 +++++++
 include/linux/soundwire/sdw.h | 5 +++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index aeaae5a57c89..b49864ca683a 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -161,7 +161,13 @@ int sdw_bus_master_add(struct sdw_bus *bus, struct device *parent,
 	bus->params.curr_dr_freq = bus->params.max_dr_freq;
 	bus->params.curr_bank = SDW_BANK0;
 	bus->params.next_bank = SDW_BANK1;
+	/*
+	 * Set is_present = true by default. It will be set to false when no peripherals
+	 * are attached on the bus.
+	 */
+	bus->is_present = true;
 
+	init_completion(&bus->enumeration_complete);
 	return 0;
 }
 EXPORT_SYMBOL(sdw_bus_master_add);
@@ -847,6 +853,7 @@ static int sdw_program_device_num(struct sdw_bus *bus, bool *programmed)
 		if (ret == -ENODATA) { /* end of device id reads */
 			dev_dbg(bus->dev, "No more devices to enumerate\n");
 			ret = 0;
+			complete_all(&bus->enumeration_complete);
 			break;
 		}
 		if (ret < 0) {
diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
index f710e5932b4b..0cb7e4fef00e 100644
--- a/include/linux/soundwire/sdw.h
+++ b/include/linux/soundwire/sdw.h
@@ -1001,6 +1001,8 @@ struct sdw_stream_runtime {
  * transport and port parameters
  * @defer_msg: Defer message
  * @params: Current bus parameters
+ * @enumeration_complete: completion utility to control potential races between
+ * enumeration completion and peripheral presence checks.
  * @stream_refcount: number of streams currently using this bus
  * @bpt_stream_refcount: number of BTP streams currently using this bus (should
  * be zero or one, multiple streams per link is not supported).
@@ -1029,6 +1031,7 @@ struct sdw_stream_runtime {
  * are supported. This flag is populated by drivers after reading
  * appropriate firmware (ACPI/DT).
  * @lane_used_bandwidth: how much bandwidth in bits per second is used by each lane
+ * @is_present: indicates whether any peripheral is present on the bus.
  */
 struct sdw_bus {
 	struct device *dev;
@@ -1042,6 +1045,7 @@ struct sdw_bus {
 	struct list_head m_rt_list;
 	struct sdw_defer defer_msg;
 	struct sdw_bus_params params;
+	struct completion enumeration_complete;
 	int stream_refcount;
 	int bpt_stream_refcount;
 	struct sdw_stream_runtime *bpt_stream;
@@ -1064,6 +1068,7 @@ struct sdw_bus {
 #endif
 	bool multi_link;
 	unsigned int lane_used_bandwidth[SDW_MAX_LANES];
+	bool is_present;
 };
 
 struct sdw_stream_runtime *sdw_alloc_stream(const char *stream_name, enum sdw_stream_type type);
-- 
2.43.0