[PATCH] Add a check for remove callback in spmi driver removal API

[Jishnu Prakash <quic_jprakash@quicinc.com>]

When removing a SPMI driver, there can be a crash due to NULL pointer
dereference if it does not have a remove callback defined, as the remove
callback gets called directly in spmi_drv_remove(). This is one such call
trace observed when removing the QCOM SPMI PMIC driver:

 dump_backtrace.cfi_jt+0x0/0x8
 dump_stack_lvl+0xd8/0x16c
 panic+0x188/0x498
 __cfi_slowpath+0x0/0x214
 __cfi_slowpath+0x1dc/0x214
 spmi_drv_remove+0x16c/0x1e0
 device_release_driver_internal+0x468/0x79c
 driver_detach+0x11c/0x1a0
 bus_remove_driver+0xc4/0x124
 driver_unregister+0x58/0x84
 cleanup_module+0x1c/0xc24 [qcom_spmi_pmic]
 __do_sys_delete_module+0x3ec/0x53c
 __arm64_sys_delete_module+0x18/0x28
 el0_svc_common+0xdc/0x294
 el0_svc+0x38/0x9c
 el0_sync_handler+0x8c/0xf0
 el0_sync+0x1b4/0x1c0

If a driver has all its resources allocated through devm_() APIs and
does not need any other explicit cleanup, it would not require a
remove callback to be defined. The SPMI framework also does not enforce
the presence of a remove callback when a client driver registers with it.
Hence, add a check for remove callback presence before calling it
when removing a SPMI driver.

Jishnu Prakash (1):
  spmi: Add a check for remove callback when removing a SPMI driver

 drivers/spmi/spmi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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2.7.4