linux-kernel - [PATCH 1/1] soundwire: bus: Don't re-enumerate before status is UNATTACHED

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Date:   Mon, 29 Aug 2022 10:44:58 +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 1/1] soundwire: bus: Don't re-enumerate before status is UNATTACHED

Don't re-enumerate a peripheral on #0 until we have seen and
handled an UNATTACHED notification for that peripheral.

Without this, it is possible for the UNATTACHED status to be missed
and so the slave->status remains at ATTACHED. If slave->status never
changes to UNATTACHED the child driver will never be notified of the
UNATTACH, and the code in sdw_handle_slave_status() will skip the
second part of enumeration because the slave->status has not changed.

This scenario can happen because PINGs are handled in a workqueue
function which is working from a snapshot of an old PING, and there
is no guarantee when this function will run.

A peripheral could report attached in the PING being handled by
sdw_handle_slave_status(), but has since reverted to device #0 and is
then found in the loop in sdw_program_device_num(). Previously the
code would not have updated slave->status to UNATTACHED because it had
not yet handled a PING where that peripheral had UNATTACHED.

This situation happens fairly frequently with multiple peripherals on
a bus that are intentionally reset (for example after downloading
firmware).

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 drivers/soundwire/bus.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index cb77da84a4f9..a3d3d66b3410 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -766,6 +766,13 @@ static int sdw_program_device_num(struct sdw_bus *bus)
 			if (sdw_compare_devid(slave, id) == 0) {
 				found = true;

+				/*
+				 * Don't re-enumerate a device until we've seen
+				 * it UNATTACH.
+				 */
+				if (slave->status != SDW_SLAVE_UNATTACHED)
+					break;
+
 				/*
 				 * Assign a new dev_num to this Slave and
 				 * not mark it present. It will be marked
-- 
2.30.2