linux-kernel - [PATCH v3 5/5] soundwire: bus: Don't exit early if no device IDs were programmed

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Message-ID: <20220914120949.747951-6-rf@opensource.cirrus.com>
Date:   Wed, 14 Sep 2022 13:09:49 +0100
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     <vkoul@...nel.org>, <yung-chuan.liao@...ux.intel.com>,
        <pierre-louis.bossart@...ux.intel.com>, <sanyog.r.kale@...el.com>
CC:     <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: [PATCH v3 5/5] soundwire: bus: Don't exit early if no device IDs were programmed

Only exit sdw_handle_slave_status() right after calling
sdw_program_device_num() if it actually programmed an ID into at
least one device.

sdw_handle_slave_status() should protect itself against phantom
device #0 ATTACHED indications. In that case there is no actual
device still on #0. The early exit relies on there being a status
change to ATTACHED on the reprogrammed device to trigger another
call to sdw_handle_slave_status() which will then handle the status
of all peripherals. If no device was actually programmed with an
ID there won't be a new ATTACHED indication. This can lead to the
status of other peripherals not being handled.

The status passed to sdw_handle_slave_status() is obviously always
from a point of time in the past, and may indicate accumulated
unhandled events (depending how the bus manager operates). It's
possible that a device ID is reprogrammed but the last PING status
captured state just before that, when it was still reporting on
ID #0. Then sdw_handle_slave_status() is called with this PING info,
just before a new PING status is available showing it now on its new
ID. So sdw_handle_slave_status() will receive a phantom report of a
device on #0, but it will not find one.

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 drivers/soundwire/bus.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index 6e569a875a9b..8eded1a55227 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -729,7 +729,7 @@ void sdw_extract_slave_id(struct sdw_bus *bus,
 }
 EXPORT_SYMBOL(sdw_extract_slave_id);
 
-static int sdw_program_device_num(struct sdw_bus *bus)
+static int sdw_program_device_num(struct sdw_bus *bus, bool *programmed)
 {
 	u8 buf[SDW_NUM_DEV_ID_REGISTERS] = {0};
 	struct sdw_slave *slave, *_s;
@@ -739,6 +739,8 @@ static int sdw_program_device_num(struct sdw_bus *bus)
 	int count = 0, ret;
 	u64 addr;
 
+	*programmed = false;
+
 	/* No Slave, so use raw xfer api */
 	ret = sdw_fill_msg(&msg, NULL, SDW_SCP_DEVID_0,
 			   SDW_NUM_DEV_ID_REGISTERS, 0, SDW_MSG_FLAG_READ, buf);
@@ -797,6 +799,8 @@ static int sdw_program_device_num(struct sdw_bus *bus)
 					return ret;
 				}
 
+				*programmed = true;
+
 				break;
 			}
 		}
@@ -1756,7 +1760,7 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 {
 	enum sdw_slave_status prev_status;
 	struct sdw_slave *slave;
-	bool attached_initializing;
+	bool attached_initializing, id_programmed;
 	int i, ret = 0;
 
 	/* first check if any Slaves fell off the bus */
@@ -1787,14 +1791,23 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 
 	if (status[0] == SDW_SLAVE_ATTACHED) {
 		dev_dbg(bus->dev, "Slave attached, programming device number\n");
-		ret = sdw_program_device_num(bus);
-		if (ret < 0)
-			dev_err(bus->dev, "Slave attach failed: %d\n", ret);
+
 		/*
-		 * programming a device number will have side effects,
-		 * so we deal with other devices at a later time
+		 * Programming a device number will have side effects,
+		 * so we deal with other devices at a later time.
+		 * This relies on those devices reporting ATTACHED, which will
+		 * trigger another call to this function. This will only
+		 * happen if at least one device ID was programmed.
+		 * Error returns from sdw_program_device_num() are currently
+		 * ignored because there's no useful recovery that can be done.
+		 * Returning the error here could result in the current status
+		 * of other devices not being handled, because if no device IDs
+		 * were programmed there's nothing to guarantee a status change
+		 * to trigger another call to this function.
 		 */
-		return ret;
+		sdw_program_device_num(bus, &id_programmed);
+		if (id_programmed)
+			return 0;
 	}
 
 	/* Continue to check other slave statuses */
-- 
2.30.2