[linux-dvb] Re: refactoring

[Andrew de Quincey <adq_dvb@lidskialf.net>]

On Sunday 10 Oct 2004 15:45, Gerd Knorr wrote:
> > Before anyone gets too excited, this was an experimental structure. I
> > think a better solution would be something like:
> >
> > struct dvb_fe {
> >  struct fe_api  *api;
> >  struct dvb_adapter *dvb;
> >  void            *priv;
> > };
> >
> > struct fe_api {
> >  struct dvb_frontend_info info;
> >
> >  void (*attach)(....)
> >  void (*set_tps)(struct dvb_fe*, struct dvb_frontend_parameters*);
> >  void (*get_tps)(struct dvb_fe*, struct dvb_frontend_parameters*);
> >  void (*get_status)(struct dvb_fe*, struct fe_status*);
> >  /* whatever else is needed, for diseqc, ... */
> >  void (*destroy)(struct dvb_fe*);
> > };
>
> Looks ok.  What attach() should do?

Actually, I found a way to do this that means we don't need the _attach() 
functions exported:

You use dvb_register_frontend()/dvb_unregister_frontend() directly to 
create/destroy frontend devices:

extern int dvb_register_frontend(struct dvb_adapter* dvb,
                                 struct dvb_frontend_ops* ops,
                                 void* adapter_data,
                                 void* demodulator_config,
                                 struct module* module,
                                 struct dvb_frontend** fe);

extern int dvb_unregister_frontend(struct dvb_frontend* fe);


Each frontend exposes an XXX_attach()/XXX_detach() function pointer, which are 
called during from the generic frontend code.

e.g. for cx22702:
static void cx22702_detach(struct dvb_frontend* fe)
{
        struct cx22702_state* state = (struct cx22702_state*) 
fe->demodulator_priv;
        kfree(state);
}

static int cx22702_attach(void* demodulator_config,
                          void** demodulator_data)
{
        struct cx22702_config* config = (struct cx22702_config*) 
demodulator_config;
        struct cx22702_state* state = NULL;
        int ret = -ENODEV;

        /* allocate memory for the internal state */
        state = (struct cx22702_state*) kmalloc(sizeof(struct cx22702_state), 
GFP_KERNEL);
        if (state == NULL) {
                ret = -ENOMEM;
                goto error;
        }

        /* setup the state */
        state->config = config;
        state->prevUCBlocks = 0;

        /* check if the demod is there */
        if (cx22702_readreg(state, 0x1f) != 0x3) goto error;

        /* ok! */
        *demodulator_data = state;
        return 0;

error:
        if (state) kfree(state);
        return ret;
}


Not all frontends need to allocate state, so they can do away with providing a 
XXX_detach() function.