[pvrusb2] New driver snapshot: pvrusb2-mci-20080210

[Mike Isely]

On Sun, 9 Mar 2008, Mark Goldberg wrote:

> On Sun, Mar 9, 2008 at 11:18 AM, Mike Isely <isely at isely.net> wrote:
> >
> >  I can tell you however that it's the programming of the video digitizer
> >  that should be affecting this.  That is controlled by either saa7115.ko
> >  or cx25840.ko (depending on if you are using a 29xxx or a 24xxx device,
> >  respectively).  The pvrusb2 driver itself doesn't directly set up
> >  details like that - it just tells the module "use video standard XYZ and
> >  I want the capture resolution to be H x V", the rest is pretty much up
> >  to the module (i.e. saa7115.ko or cx25840.ko).  This is why I'm doubtful
> >  that recent pvrusb2 driver changes could be responsible.  This
> >  unfortunately doesn't align with your observations, so I really have no
> >  idea what is going on here.
> 
> It's a cx25840.
> 
> How can I see what is getting passed? When is it done? I can do some debugging.
> 
> If you remember the order of module loading changed on my system with the new
> snapshot and I have to add video_nr=2 to get it to load at the right
> time. Maybe the
> load order is keeping it from intiializing at the right time or maybe
> it is getting initialized
> again wrong. Or, is the initialization at capture time?

Initialization order should have nothing to do with it.  Once the 
pvrusb2 driver is told about the new device, it sets up communications 
with it.  As part of that process, the driver initialization an I2C 
adapter abstraction in the kernel.  When that happens, various 
registered I2C modules (e.g. cx25840) probe the bus and initialize 
themselves when they find the part they are looking for.  So the 
initialization and operation of the cx25843 chip in your device is 
pretty much autonomous with respect to the pvrusb2 driver - once the 
driver initializes that I2C adapter.  And in that respect it should not 
matter if you are dealing with /dev/video0, /dev/video1, or /dev/video2.  

Once the cx25840 module has begun talking to the chip, then it can do 
whatever communication it wants with it at any time.  It's entirely up 
to the module.  For example, the lirc_i2c module will perform continuous 
polls of the IR receiver chip in order to catch incoming IR codes.  The 
cx25840 module is going to do a whole pile of transactions up front, 
first to send its chip a piece of firmware, then to initialize a mess of 
registers in the chip.  This action is *completely* up to the cx25840 
module, not the pvrusb2 driver.  Once initialization is complete, then 
generally a module like cx25840 is going to go idle until such time as 
it sees activity from the pvrusb2 driver - there's a sort of a "bus" 
where the pvrusb2 where the pvrusb2 driver can put stuff out there to be 
noticed by these modules.  For example, "set frequency" or "set video 
standard", or "begin capture".  When the cx25840 module sees these 
things it is going to react by performing more transactions with its 
chip, in order to implement the effect of those actions.

For the record, this description also applies to saa7115 (for 29xxx 
devices), except in that case there's no firmware to load.

As for being able to trace the cx25840 module, there are some hackish 
things we can do in the pvrusb2 driver to snoop the I2C traffic between 
the cx25840 module and the part it is controlling.  I've had to do that 
in the past in order to debug other problems (usually with stuck 
hardware).  But a more fruitful strategy might be to turn on debugging 
within the cx2540 module itself.  All these modules generally have a 
"debug" parameter you can set.  Depending on the module, that will help 
show what is going on.  However I have to warn you that for the sort of 
thing you are looking for, you will likely want to have the chip's 
datasheet in front of you when you do this, and this is not a simple 
part :-( The PDF I have for it is 289 pages.

Does this help with understanding things or have I muddied it up?

  -Mike

-- 

Mike Isely
isely @ pobox (dot) com
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