[linux-dvb] [PATCH] make the registers of the stv0297 visible for other applications (e.g. i2cdump)

Johannes Stezenbach js at linuxtv.org
Sat Jun 2 11:24:15 CEST 2007


On Fri, Jun 01, 2007, Oliver Endriss wrote:
> e9hack wrote:
> > Manu Abraham wrote:
> > > e9hack wrote:
> > >> Manu Abraham wrote:
> > >>> Trent Piepho wrote:
> > >>>> What the stv0297 wants is:
> > >>>> S Addr Wr [A] Comm [A] P S Addr Rd [A] [Data] NA P
> > >>>>  
> > >>> The STV0297 is just a normal demod like the others, nothing special
> > >>> about it (according to ST). Well of course i2cdump can be wrong.
> > >> The stv0297 cannot handle a repeated start condition and it needs
> > >> a little delay between the stop and the next start condition. A
> > >> stop and a start condition cannot be on the same upload command
> > >> of a saa7146 (on a TT 2300C).
> > > 
> > > Any idea what the SAA7146 - STV0297 windows driver does ?
> > > 
> > 
> > Good point. I can monitor any access to the saa7146 registers of the
> > TT 2300C on Windows. I will check this issue. In the past, I was
> > more interested in the high level part of the i2c-communication.
> 
> Any news about this?
> 
> Imho Trent's patch to add I2C_M_STOP makes sense.
> 
> According to the stv0299 datasheet, the stv0299 requires this STOP
> condition, too. This chip seems to be more tolerant though.
> The current driver does not send STOP before READ, and it works.

I re-read the i2c spec (conveniently available from
http://i2c-bus.org/ ), and although it doesn't use very
clear words I think it says that any device _must_ support
repeated start conditions (e.g. section 9 FORMATS WITH 7-BIT
ADDRESSES).

There's also some more explanation:
http://i2c-bus.org/RepeatedStartCondition/

Now, it could well be that the stv0297 i2c interface
is broken (broken because it cannot safely be used on a bus
with multiple masters), but it may also be quite possible
that the stv0297 datasheet is just inaccurate.

IMHO both possibilities are just as likely, however I trust
adq has actually tested that repeat start doesn't work.
http://linuxtv.org/hg/v4l-dvb/rev/c204a1d063aa

Then I2C_M_STOP still makes sense, but the patch should document
that it's used only a workaround for broken hardware.


Regards,
Johannes



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