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From:   James Clark <james.clark@arm.com>
To:     coresight@lists.linaro.org, quic_jinlmao@quicinc.com,
        mike.leach@linaro.org, suzuki.poulose@arm.com
Cc:     James Clark <james.clark@arm.com>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Leo Yan <leo.yan@linaro.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: [PATCH v5 01/13] coresight: Fix loss of connection info when a module is unloaded
Date:   Tue,  4 Apr 2023 16:51:07 +0100
Message-Id: <20230404155121.1824126-2-james.clark@arm.com>
In-Reply-To: <20230404155121.1824126-1-james.clark@arm.com>
References: <20230404155121.1824126-1-james.clark@arm.com>
MIME-Version: 1.0
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child_fwnode should be a read only property based on the DT or ACPI. If
it's cleared on the parent device when a child is unloaded, then when
the child is loaded again the connection won't be remade.

child_dev should be cleared instead which signifies that the connection
should be remade when the child_fwnode registers a new coresight_device.

Similarly the reference count shouldn't be decremented as long as the
parent device exists. The correct place to drop the reference is in
coresight_release_platform_data() which is already done.

Reproducible on Juno with the following steps:

  # load all coresight modules.
  $ cd /sys/bus/coresight/devices/
  $ echo 1 > tmc_etr0/enable_sink
  $ echo 1 > etm0/enable_source
  # Works fine ^

  $ echo 0 > etm0/enable_source
  $ rmmod coresight-funnel
  $ modprobe coresight-funnel
  $ echo 1 > etm0/enable_source
  -bash: echo: write error: Invalid argument

Fixes: 37ea1ffddffa ("coresight: Use fwnode handle instead of device names")
Fixes: 2af89ebacf29 ("coresight: Clear the connection field properly")
Tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: James Clark <james.clark@arm.com>
---
 drivers/hwtracing/coresight/coresight-core.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index d3bf82c0de1d..5733294ce5cd 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -1419,13 +1419,8 @@ static int coresight_remove_match(struct device *dev, void *data)
 		if (csdev->dev.fwnode == conn->child_fwnode) {
 			iterator->orphan = true;
 			coresight_remove_links(iterator, conn);
-			/*
-			 * Drop the reference to the handle for the remote
-			 * device acquired in parsing the connections from
-			 * platform data.
-			 */
-			fwnode_handle_put(conn->child_fwnode);
-			conn->child_fwnode = NULL;
+
+			conn->child_dev = NULL;
 			/* No need to continue */
 			break;
 		}
-- 
2.34.1