soundwire: cadence_master: add hw_reset capability in debugfs

Provide debugfs capability to kick link and devices into hard-reset
(as defined by MIPI). This capability is really useful when some
devices are no longer responsive and/or to check the software handling
of resynchronization.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20191022235448.17586-3-pierre-louis.bossart@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/cadence_master.c

@@ -333,6 +333,26 @@ static int cdns_reg_show(struct seq_file *s, void *data)
 }
 DEFINE_SHOW_ATTRIBUTE(cdns_reg);
 
+static int cdns_hw_reset(void *data, u64 value)
+{
+	struct sdw_cdns *cdns = data;
+	int ret;
+
+	if (value != 1)
+		return -EINVAL;
+
+	/* Userspace changed the hardware state behind the kernel's back */
+	add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+
+	ret = sdw_cdns_exit_reset(cdns);
+
+	dev_dbg(cdns->dev, "link hw_reset done: %d\n", ret);
+
+	return ret;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(cdns_hw_reset_fops, NULL, cdns_hw_reset, "%llu\n");
+
 /**
  * sdw_cdns_debugfs_init() - Cadence debugfs init
  * @cdns: Cadence instance
@@ -341,6 +361,9 @@ DEFINE_SHOW_ATTRIBUTE(cdns_reg);
 void sdw_cdns_debugfs_init(struct sdw_cdns *cdns, struct dentry *root)
 {
 	debugfs_create_file("cdns-registers", 0400, root, cdns, &cdns_reg_fops);
+
+	debugfs_create_file("cdns-hw-reset", 0200, root, cdns,
+			    &cdns_hw_reset_fops);
 }
 EXPORT_SYMBOL_GPL(sdw_cdns_debugfs_init);