[linux-dvb] Changes to FE_REGISTER/FE_UNREGISTER calling convention

[Ralph Metzler <rjkm@metzlerbros.de>]

Christopher Pascoe writes:
 > At first I was looking at removing FE_UNREGISTER completely, and
 > triggering all the actions from the but this still has problems in the
 > case of multi-function cards with separate modules - unloading the DVB
 > module can result in a similar behaviour, with an oops as the dvb_adapter
 > handle that we kept is no longer valid.
 > 
 > I propose the following changes to address these problems:
 > 
 > 1. Frontend's .attach_adapter is modified to probe the i2c bus and check
 > to see if it will be possible to attach a DVB tuner on this device.  If
 > so, performs an i2c_attach_client and returns.  Remove the
 > BUG_ON(!state->dvb) and the call to dvb_register_frontend, leaving us
 > attached to receive a FE_REGISTER later on.
 > 
 > 2. Frontend's .command routine is modified to call dvb_register_frontend
 > as a result of a FE_REGISTER call iff (state->dvb == NULL).
 > 
 > 3. Card's driver is modified to performs an i2c_clients_command(..,
 > FE_REGISTER, dvb_adapter) in its core attach_inform routine (should it be
 > already ready to handle DVB (i.e. in the multi-module case, when the DVB
 > module is loaded)) and in its probe routine (immediately after it
 > registers its frontends, etc, to the DVB core).
 > 
 > 4. Card's driver is modified to perform i2c_clients_command(..,
 > FE_UNREGISTER, dvb_adapter) from its core detach_inform routine, and its
 > DVB module to call i2c_clients_command(.., FE_UNREGISTER, dvb_adapter)
 > from its .remove routine before unregistering itself from the DVB core.
 > 
 > 5. Frontend's .command routine modified to perform a
 > dvb_unregister_frontend() if state->dvb == the state->dvb we were passed
 > and sets state->dvb to NULL.
 > 
 > 6. Frontend's .detach_client routine calls dvb_unregister_frontend() if
 > state->dvb is set, and then calls i2c_detach_client().  This
 > unregister_frontend is needed as i2c_clients_command won't send a
 > FE_UNREGISTER message to a driver that in the process of being unloaded.
 > 
 > I think that this permits all orderings of frontend/core/dvb module
 > load/unloads without oopsing.  I have made such changes to the cx88 and
 > mt352 modules and tested various combinations of module loads/unloads with
 > no ill effect.
 > 
 > Does anyone have any comments on this?  If this looks good, I will put
 > together a patch for all the frontends/cx88/bt8xx cards to make them
 > behave in this way.

Sounds fine.
This is all (except for point 6) as I always implemented it. I don't
know why this was done differently in the linuxtv version.

Strangly, the case in point 6 does not happen for me.
I tested it and the client command comes through although it should not. 
try_module_get() in i2c_clients_command() should fail during a
module exit but it does not ...


Ralph