[linux-dvb] Re: V4L issues with linux dvb driver

[Michael Hunold <hunold-ml@web.de>]

Hello Billy,

> I'll have a look at this later today and test the "dvb-kernel" driver 
> with "tvtime" and come back to you later.
Ok, I see that "tvterm" uses plain v4l, so it should work through the 
compatibility layer.

Unfortunately, the driver does not support the 
"old-style-mmap()-interface" through the compatiblity layer. 8-(

"Old style" means, that all capture buffers are mmap()ed in a single 
call, the buffers are separated by offsets. Using v4l2, you mmap() every 
single buffer individually. For the compatibility layer to work, you 
need some extra hooks, that are not present in the current driver.

This is the reason, why "tvtime" only gets one capture buffer and that's 
why the performance sucks.

Two solutions:
1) Add these extra hooks to the driver, so the compatiblity layer is 
satisfied.

I don't like this solution, because there are many more problems 
regarding the interaction between saa7146 and v4l. One example: your 
driver expects hue/brightness/colour/contrast, while the saa7146 
delivers brightness/constrast/saturation only...

2) Switch to v4l2. Drivers are available for all common chipsets (bt8x8, 
saa7134, saa7146), they will be part of the 2.6.x kernel by default.

To support this, I made a quick-and-dirty hack porting "tvtime" to v4l2. 
I fixed most stuff to PAL and threw out everything that's not needed. 
Some quirks were necessary to squeeze the v4l1 capture scheme to the way 
v4l2 works. The subsystem should be redesigned though.

I attached a diff to the current CVS to this mail. You need to put 
"videodev2.h" for example to /usr/include/linux.

CU
Michael.

Attachment: tvtime_v4l2.diff.gz
Description: GNU Zip compressed data