[alsa-devel] [PATCH v3 4/4] soundwire: intel: handle disabled links

[Pierre-Louis Bossart]

On most hardware platforms, SoundWire interfaces are pin-muxed with
other interfaces (typically DMIC or I2S) and the status of each link
needs to be checked at boot time.

For Intel platforms, the BIOS provides a menu to enable/disable the
links separately, and the information is provided to the OS with an
Intel-specific _DSD property. The same capability will be added to
revisions of the MIPI DisCo specification.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
---
 drivers/soundwire/intel.c     | 26 ++++++++++++++++++++++----
 include/linux/soundwire/sdw.h |  2 ++
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/soundwire/intel.c b/drivers/soundwire/intel.c
index 3faa9678c715..f1e38a293967 100644
--- a/drivers/soundwire/intel.c
+++ b/drivers/soundwire/intel.c
@@ -91,6 +91,8 @@
 #define SDW_ALH_STRMZCFG_DMAT		GENMASK(7, 0)
 #define SDW_ALH_STRMZCFG_CHN		GENMASK(19, 16)
 
+#define SDW_INTEL_QUIRK_MASK_BUS_DISABLE	BIT(1)
+
 enum intel_pdi_type {
 	INTEL_PDI_IN = 0,
 	INTEL_PDI_OUT = 1,
@@ -944,7 +946,7 @@ static int sdw_master_read_intel_prop(struct sdw_bus *bus)
 	struct sdw_master_prop *prop = &bus->prop;
 	struct fwnode_handle *link;
 	char name[32];
-	int nval, i;
+	u32 quirk_mask;
 
 	/* Find master handle */
 	snprintf(name, sizeof(name),
@@ -959,6 +961,14 @@ static int sdw_master_read_intel_prop(struct sdw_bus *bus)
 	fwnode_property_read_u32(link,
 				 "intel-sdw-ip-clock",
 				 &prop->mclk_freq);
+
+	fwnode_property_read_u32(link,
+				 "intel-quirk-mask",
+				 &quirk_mask);
+
+	if (quirk_mask & SDW_INTEL_QUIRK_MASK_BUS_DISABLE)
+		prop->hw_disabled = true;
+
 	return 0;
 }
 
@@ -1019,6 +1029,12 @@ static int intel_probe(struct platform_device *pdev)
 		goto err_master_reg;
 	}
 
+	if (sdw->cdns.bus.prop.hw_disabled) {
+		dev_info(&pdev->dev, "SoundWire master %d is disabled, ignoring\n",
+			 sdw->cdns.bus.link_id);
+		return 0;
+	}
+
 	/* Initialize shim and controller */
 	intel_link_power_up(sdw);
 	intel_shim_init(sdw);
@@ -1072,9 +1088,11 @@ static int intel_remove(struct platform_device *pdev)
 
 	sdw = platform_get_drvdata(pdev);
 
-	intel_debugfs_exit(sdw);
-	free_irq(sdw->res->irq, sdw);
-	snd_soc_unregister_component(sdw->cdns.dev);
+	if (!sdw->cdns.bus.prop.hw_disabled) {
+		intel_debugfs_exit(sdw);
+		free_irq(sdw->res->irq, sdw);
+		snd_soc_unregister_component(sdw->cdns.dev);
+	}
 	sdw_delete_bus_master(&sdw->cdns.bus);
 
 	return 0;
diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
index 2028318a4c62..be9fe08d4e9c 100644
--- a/include/linux/soundwire/sdw.h
+++ b/include/linux/soundwire/sdw.h
@@ -380,6 +380,7 @@ struct sdw_slave_prop {
  * @err_threshold: Number of times that software may retry sending a single
  * command
  * @mclk_freq: clock reference passed to SoundWire Master, in Hz.
+ * @hw_disabled: if true, the Master is not functional, typically due to pin-mux
  */
 struct sdw_master_prop {
 	u32 revision;
@@ -395,6 +396,7 @@ struct sdw_master_prop {
 	bool dynamic_frame;
 	u32 err_threshold;
 	u32 mclk_freq;
+	bool hw_disabled;
 };
 
 int sdw_master_read_prop(struct sdw_bus *bus);
-- 
2.20.1