soundwire: cadence: only prepare attached devices on clock stop

We sometimes see COMMAND_IGNORED responses during the clock stop
sequence. It turns out we already have information if devices are
present on a link, so we should only prepare those when they
are attached.

In addition, even when COMMAND_IGNORED are received, we should still
proceed with the clock stop. The device will not be prepared but
that's not a problem.

The only case where the clock stop will fail is if the Cadence IP
reports an error (including a timeout), or if the devices throw a
COMMAND_FAILED response.

BugLink: thesofproject#2621
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20210323013707.21455-1-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/cadence_master.c

@@ -1450,10 +1450,12 @@ int sdw_cdns_clock_stop(struct sdw_cdns *cdns, bool block_wake)
 	}
 
 	/* Prepare slaves for clock stop */
-	ret = sdw_bus_prep_clk_stop(&cdns->bus);
-	if (ret < 0) {
-		dev_err(cdns->dev, "prepare clock stop failed %d", ret);
-		return ret;
+	if (slave_present) {
+		ret = sdw_bus_prep_clk_stop(&cdns->bus);
+		if (ret < 0 && ret != -ENODATA) {
+			dev_err(cdns->dev, "prepare clock stop failed %d\n", ret);
+			return ret;
+		}
 	}
 
 	/*