ASoC: SOF: Intel: hda-mlink: add helper to retrieve eml_lock

For SoundWire usages, we need to use the global eml_lock to
serialize/protect all accesses to shared registers.  Due to the split
implementation across two subsystems, we need to pass a pointer
around.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20230404104127.5629-19-peter.ujfalusi@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

include/sound/hda-mlink.h

@@ -52,6 +52,8 @@ int hda_bus_ml_suspend(struct hdac_bus *bus);
 struct hdac_ext_link *hdac_bus_eml_ssp_get_hlink(struct hdac_bus *bus);
 struct hdac_ext_link *hdac_bus_eml_dmic_get_hlink(struct hdac_bus *bus);
 
+struct mutex *hdac_bus_eml_get_mutex(struct hdac_bus *bus, bool alt, int elid);
+
 int hdac_bus_eml_enable_offload(struct hdac_bus *bus, bool alt, int elid, bool enable);
 
 #else
@@ -153,6 +155,9 @@ hdac_bus_eml_ssp_get_hlink(struct hdac_bus *bus) { return NULL; }
 static inline struct hdac_ext_link *
 hdac_bus_eml_dmic_get_hlink(struct hdac_bus *bus) { return NULL; }
 
+static inline struct mutex *
+hdac_bus_eml_get_mutex(struct hdac_bus *bus, bool alt, int elid) { return NULL; }
+
 static inline int
 hdac_bus_eml_enable_offload(struct hdac_bus *bus, bool alt, int elid, bool enable)
 {

sound/soc/sof/intel/hda-mlink.c

@@ -800,6 +800,18 @@ int hda_bus_ml_suspend(struct hdac_bus *bus)
 }
 EXPORT_SYMBOL_NS(hda_bus_ml_suspend, SND_SOC_SOF_HDA_MLINK);
 
+struct mutex *hdac_bus_eml_get_mutex(struct hdac_bus *bus, bool alt, int elid)
+{
+	struct hdac_ext2_link *h2link;
+
+	h2link = find_ext2_link(bus, alt, elid);
+	if (!h2link)
+		return NULL;
+
+	return &h2link->eml_lock;
+}
+EXPORT_SYMBOL_NS(hdac_bus_eml_get_mutex, SND_SOC_SOF_HDA_MLINK);
+
 struct hdac_ext_link *hdac_bus_eml_ssp_get_hlink(struct hdac_bus *bus)
 {
 	struct hdac_ext2_link *h2link;