coresight: Fix crash when Perf and sysfs modes are used concurrently

[ Upstream commit 287e82cf ]

Partially revert the change in commit 61486528 ("coresight: Enable
and disable helper devices adjacent to the path") which changed the bare
call from source_ops(csdev)->enable() to coresight_enable_source() for
Perf sessions. It was missed that coresight_enable_source() is
specifically for the sysfs interface, rather than being a generic call.
This interferes with the sysfs reference counting to cause the following
crash:

  $ perf record -e cs_etm/@tmc_etr0/ -C 0 &
  $ echo 1 > /sys/bus/coresight/devices/tmc_etr0/enable_sink
  $ echo 1 > /sys/bus/coresight/devices/etm0/enable_source
  $ echo 0 > /sys/bus/coresight/devices/etm0/enable_source

  Unable to handle kernel NULL pointer dereference at virtual
  address 00000000000001d0
  Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
  ...
  Call trace:
   etm4_disable+0x54/0x150 [coresight_etm4x]
   coresight_disable_source+0x6c/0x98 [coresight]
   coresight_disable+0x74/0x1c0 [coresight]
   enable_source_store+0x88/0xa0 [coresight]
   dev_attr_store+0x20/0x40
   sysfs_kf_write+0x4c/0x68
   kernfs_fop_write_iter+0x120/0x1b8
   vfs_write+0x2dc/0x3b0
   ksys_write+0x70/0x108
   __arm64_sys_write+0x24/0x38
   invoke_syscall+0x50/0x128
   el0_svc_common.constprop.0+0x104/0x130
   do_el0_svc+0x40/0xb8
   el0_svc+0x2c/0xb8
   el0t_64_sync_handler+0xc0/0xc8
   el0t_64_sync+0x1a4/0x1a8
  Code: d53cd042 91002000 b9402a81 b8626800 (f940ead5)
  ---[ end trace 0000000000000000 ]---

This commit linked below also fixes the issue, but has unlocked updates
to the mode which could potentially race. So until we come up with a
more complete solution that takes all locking and interaction between
both modes into account, just revert back to the old behavior for Perf.

Reported-by: Junhao He <hejunhao3@huawei.com>
Closes: https://lore.kernel.org/linux-arm-kernel/20230921132904.60996-1-hejunhao3@huawei.com/


Fixes: 61486528 ("coresight: Enable and disable helper devices adjacent to the path")
Tested-by: Junhao He <hejunhao3@huawei.com>
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/20231006131452.646721-1-james.clark@arm.com


Signed-off-by: Sasha Levin <sashal@kernel.org>