soundwire: cadence: add debugfs interface for PDI loopbacks

For debug, it's interesting to create a loopback stream for each link
and use debugfs to set a source and target PDI. The target PDI would
need to be an RX port and use the same register configurations as the
source PDI. This capability allows e.g. for the headphone playback
stream to be snooped on the headset capture stream, or alternatively
for the addition of a dedicated loopback stream, in addition of
regular capture for that link.

This patch only adds the debugfs part, the port/PDI handling will be
handled in the next patches.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20210714032209.11284-10-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/cadence_master.c

@@ -450,6 +450,40 @@ static int cdns_parity_error_injection(void *data, u64 value)
 DEFINE_DEBUGFS_ATTRIBUTE(cdns_parity_error_fops, NULL,
 			 cdns_parity_error_injection, "%llu\n");
 
+static int cdns_set_pdi_loopback_source(void *data, u64 value)
+{
+	struct sdw_cdns *cdns = data;
+	unsigned int pdi_out_num = cdns->pcm.num_bd + cdns->pcm.num_out;
+
+	if (value > pdi_out_num)
+		return -EINVAL;
+
+	/* Userspace changed the hardware state behind the kernel's back */
+	add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+
+	cdns->pdi_loopback_source = value;
+
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(cdns_pdi_loopback_source_fops, NULL, cdns_set_pdi_loopback_source, "%llu\n");
+
+static int cdns_set_pdi_loopback_target(void *data, u64 value)
+{
+	struct sdw_cdns *cdns = data;
+	unsigned int pdi_in_num = cdns->pcm.num_bd + cdns->pcm.num_in;
+
+	if (value > pdi_in_num)
+		return -EINVAL;
+
+	/* Userspace changed the hardware state behind the kernel's back */
+	add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+
+	cdns->pdi_loopback_target = value;
+
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(cdns_pdi_loopback_target_fops, NULL, cdns_set_pdi_loopback_target, "%llu\n");
+
 /**
  * sdw_cdns_debugfs_init() - Cadence debugfs init
  * @cdns: Cadence instance
@@ -464,6 +498,16 @@ void sdw_cdns_debugfs_init(struct sdw_cdns *cdns, struct dentry *root)
 
 	debugfs_create_file("cdns-parity-error-injection", 0200, root, cdns,
 			    &cdns_parity_error_fops);
+
+	cdns->pdi_loopback_source = -1;
+	cdns->pdi_loopback_target = -1;
+
+	debugfs_create_file("cdns-pdi-loopback-source", 0200, root, cdns,
+			    &cdns_pdi_loopback_source_fops);
+
+	debugfs_create_file("cdns-pdi-loopback-target", 0200, root, cdns,
+			    &cdns_pdi_loopback_target_fops);
+
 }
 EXPORT_SYMBOL_GPL(sdw_cdns_debugfs_init);
 

drivers/soundwire/cadence_master.h

@@ -129,6 +129,9 @@ struct sdw_cdns {
 	struct sdw_cdns_streams pcm;
 	struct sdw_cdns_streams pdm;
 
+	int pdi_loopback_source;
+	int pdi_loopback_target;
+
 	void __iomem *registers;
 
 	bool link_up;