coresight: Fix loss of connection info when a module is unloaded
authorJames Clark <james.clark@arm.com>
Tue, 25 Apr 2023 14:35:28 +0000 (15:35 +0100)
committerSuzuki K Poulose <suzuki.poulose@arm.com>
Mon, 5 Jun 2023 14:46:45 +0000 (15:46 +0100)
commitc45b2835e7b205783bdfe08cc98fa86a7c5eeb74
treef3f0618020d7f85e7dd7ec499fedab16f9599d11
parentd388f06aced3b9fe2fb167f48ceedf75ea7629f8
coresight: Fix loss of connection info when a module is unloaded

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>
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: James Clark <james.clark@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230425143542.2305069-2-james.clark@arm.com
drivers/hwtracing/coresight/coresight-core.c