Re: prototype of a USB v4l2 driver? gspca?

[Hans de Goede <j.w.r.degoede@hhs.nl>]

Markus Rechberger wrote:
> On Sun, Jul 13, 2008 at 9:29 PM, Hans de Goede <j.w.r.degoede@hhs.nl> wrote:
>> Andrea wrote:
>>> Hans de Goede wrote:
>>>> Andrea wrote:
>>>>
>>>> What kind of device, I think that for webcams you;re best using gspca,
>>>> (now merged in mecurial), that handles all the usb specific stuff, buffer
>>>> management, etc. In general it makes it easy to write a webcam driver
>>>> allowing you to focus on the interaction with the cam, rather then having to
>>>> worry about looking, usb specifics, buffer management etc.
>>>>
>>> I've had a quick look at the structure of gspca, and it seems that any
>>> subdriver should just (easier to say that to do) fill one of those
>>> structures
>>>
>> Correct.
>>
>>> struct sd_desc {
>>> /* information */
>>>    const char *name;    /* sub-driver name */
>>> /* controls */
>>>    const struct ctrl *ctrls;
>>>    int nctrls;
>>> /* operations */
>>>    cam_cf_op config;    /* called on probe */
>>>    cam_op open;        /* called on open */
>>>    cam_v_op start;        /* called on stream on */
>>>    cam_v_op stopN;        /* called on stream off - main alt */
>>>    cam_v_op stop0;        /* called on stream off - alt 0 */
>>>    cam_v_op close;        /* called on close */
>>>    cam_pkt_op pkt_scan;
>>> /* optional operations */
>>>    cam_v_op dq_callback;    /* called when a frame has been dequeued */
>>>    cam_jpg_op get_jcomp;
>>>    cam_jpg_op set_jcomp;
>>>    cam_qmnu_op querymenu;
>>> };
>>>
>>> 1) providing ctrls (+ functions to handle settings)
>>> 2) functions to open/stream/close etc...
>>>
>>> It does not seem too bad.
>>>
>> It isn't.
>>
>>> The a natural question that comes to me:
>>>
>>> Shouldn't many more USB drivers be implemented as subdrivers of gspca?
>> Yes that would remove lots of code duplication, but allas they were written
>> before gspca (version 2, as you currently see in mercurial) was around.
>>
> 
> I guess quite a few drivers have extra features which might be missing
> in other usb based ones. Best is probably to have a look at all
> available ones and cherry pick the best ideas and easiest to
> understand parts.
> I think they are all on a certain level of quality right now.
> 
> * gspca
> * uvcvideo
> * em28xx from mcentral.de
> 

Well these 3 drivers (in case of gscpa driver group) target different classes 
of hardware:
gspca:     pre uvc webcams (and nothing more then that)
uvcvideo:  uvc devices
em28xx:    em28xx based devices, which can be dvd, analogtv, webcam, etc, etc.

Regards,

Hans

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