soundwire: stream: Fix test for DP prepare complete

In sdw_prep_deprep_slave_ports(), after the wait_for_completion()
the DP prepare status register is read. If this indicates that the
port is now prepared, the code should continue with the port setup.
It is irrelevant whether the wait_for_completion() timed out if the
port is now ready.

The previous implementation would always fail if the
wait_for_completion() timed out, even if the port was reporting
successful prepare.

This patch also fixes a minor bug where the return from sdw_read()
was not checked for error - any error code with LSBits clear could
be misinterpreted as a successful port prepare.

Fixes: 79df15b ("soundwire: Add helpers for ports operations")
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210618144745.30629-1-rf@opensource.cirrus.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: rfvirgil

drivers/soundwire/stream.c

@@ -422,7 +422,6 @@ static int sdw_prep_deprep_slave_ports(struct sdw_bus *bus,
 	struct completion *port_ready;
 	struct sdw_dpn_prop *dpn_prop;
 	struct sdw_prepare_ch prep_ch;
-	unsigned int time_left;
 	bool intr = false;
 	int ret = 0, val;
 	u32 addr;
@@ -479,15 +478,15 @@ static int sdw_prep_deprep_slave_ports(struct sdw_bus *bus,
 
 		/* Wait for completion on port ready */
 		port_ready = &s_rt->slave->port_ready[prep_ch.num];
-		time_left = wait_for_completion_timeout(port_ready,
-				msecs_to_jiffies(dpn_prop->ch_prep_timeout));
+		wait_for_completion_timeout(port_ready,
+			msecs_to_jiffies(dpn_prop->ch_prep_timeout));
 
 		val = sdw_read(s_rt->slave, SDW_DPN_PREPARESTATUS(p_rt->num));
-		val &= p_rt->ch_mask;
-		if (!time_left || val) {
+		if ((val < 0) || (val & p_rt->ch_mask)) {
+			ret = (val < 0) ? val : -ETIMEDOUT;
 			dev_err(&s_rt->slave->dev,
-				"Chn prep failed for port:%d\n", prep_ch.num);
-			return -ETIMEDOUT;
+				"Chn prep failed for port %d: %d\n", prep_ch.num, ret);
+			return ret;
 		}
 	}