Re: [PATCH 2/3] dvb-usb: multi-frontend support (MFE)

[Antti Palosaari <crope@iki.fi>]

On 08/01/2011 03:46 AM, Mauro Carvalho Chehab wrote:
> Em 27-07-2011 16:49, Antti Palosaari escreveu:
>> On 07/27/2011 10:06 PM, Mauro Carvalho Chehab wrote:
>>
>>>> +    for (i = 0; i<= x; i++) {
>>>> +        ret = adap->props.frontend_attach(adap);
>>>> +        if (ret || adap->fe[i] == NULL) {
>>>> +            /* only print error when there is no FE at all */
>>>> +            if (i == 0)
>>>> +                err("no frontend was attached by '%s'",
>>>> +                    adap->dev->desc->name);
>>>
>>> This doesn't seem right. One thing is to accept adap->fe[1] to be
>>> NULL. Another thing is to accept an error at the attach. IMO, the
>>> logic should be something like:
>>>
>>>     if (ret<  0)
>>>         return ret;
>>>
>>>     if (!i&&  !adap->fe[0]) {
>>>         err("no adapter!");
>>>         return -ENODEV;
>>>     }
>>
>> Heh, I tried to keep it functioning as earlier not to break anything! Only thing it does now differently is that it keeps silent when 2nd FE attach fails since we don't know always before fe attach if there is fe or not.
>>
>> So since it *does not change old behaviour* it must be OK. Let fix old problems later. There is millions of DVB USB callbacks failing silently - like tuner_attach etc.
>>
>> Surely I want also fix many old issues but it is always too risky.
> 
> Added support for DRX-K way at dvb-usb:
> 
> http://git.linuxtv.org/mchehab/experimental.git/commitdiff/765b3db218f1e9af6432251c2ebe59bc9660cd42
> http://git.linuxtv.org/mchehab/experimental.git/commitdiff/37fa5797c58068cc60cca6829bd662cd4f883cfa
> 
> One bad thing I noticed with the API is that it calls adap->props.frontend_attach(adap)
> several times, instead of just one, without even passing an argument for the driver to
> know that it was called twice.
> 
> IMO, there are two ways of doing the attach:
> 
> 1) call it only once, and, inside the driver, it will loop to add the other FE's;
> 2) add a parameter, at the call, to say what FE needs to be initialized.
> 
> I think (1) is preferred, as it is more flexible, allowing the driver to test for
> several types of frontends.

For more you add configuration parameters more it goes complex. Now it
calls attach as many times as .num_frontends is set in adapter
configuration. It is currently only DRX-K frontend which does not behave
like other FEs. You have added similar hacks to em28xx and now DVB USB.
Maybe it could be easier to change DRX-K driver to attach and register
as others. Also I see it very easy at least in theory to register as one
DRX-K FE normally and then hack 2nd FE in device driver (which is I
think done other drivers using that chip too).


regards
Antti
-- 
http://palosaari.fi/