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Re: [PATCH v2 00/26] Improve DVB documentation and reduce its gap

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Em Mon, 4 Sep 2017 09:12:49 +0200
Honza Petrouš <jpetrous@gmail.com> escreveu:

> 2017-09-04 2:54 GMT+02:00 Mauro Carvalho Chehab <mchehab@s-opensource.com>:
> > Em Sun, 3 Sep 2017 22:05:23 +0200
> > Honza Petrouš <jpetrous@gmail.com> escreveu:
> >  
> >> 1) #define CA_SET_DESCR      _IOW('o', 134, ca_descr_t)
> >> ============================================
> >>
> >> CA_SET_DESCR is used for feeding descrambler device
> >> with correct keys (called here "control words") what
> >> allows to get services unscrambled.
> >>
> >> The best docu is:
> >>
> >> "Digital Video Broadcasting (DVB);
> >> Support for use of the DVB Scrambling Algorithm version 3
> >> within digital broadcasting systems"
> >>
> >> Defined as DVB Document A125 and publicly
> >> available here:
> >>
> >> https://www.dvb.org/resources/public/standards/a125_dvb-csa3.pdf
> >>
> >>
> >> typedef struct ca_descr {
> >>         unsigned int index;
> >>         unsigned int parity;    /* 0 == even, 1 == odd */
> >>         unsigned char cw[8];
> >> } ca_descr_t;
> >>
> >> The 'index' is adress of the descrambler instance, as there exist
> >> limited number of them (retieved by CA_GET_DESCR_INFO).  
> >
> > Thanks for the info. If I understood well, the enclosed patch should
> > be documenting it.
> >
> >
> > Thanks,
> > Mauro
> >
> > [PATCH] media: ca docs: document CA_SET_DESCR ioctl and structs
> >
> > The av7110 driver uses CA_SET_DESCR to store the descrambler
> > control words at the CA descrambler slots.
> >
> > Document it.
> >
> > Thanks-to: Honza Petrouš <jpetrous@gmail.com>
> > Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
> >
> > diff --git a/Documentation/media/uapi/dvb/ca-set-descr.rst b/Documentation/media/uapi/dvb/ca-set-descr.rst
> > index 9c484317d55c..a6c47205ffd8 100644
> > --- a/Documentation/media/uapi/dvb/ca-set-descr.rst
> > +++ b/Documentation/media/uapi/dvb/ca-set-descr.rst
> > @@ -28,22 +28,11 @@ Arguments
> >  ``msg``
> >    Pointer to struct :c:type:`ca_descr`.
> >
> > -.. c:type:: ca_descr
> > -
> > -.. code-block:: c
> > -
> > -    struct ca_descr {
> > -       unsigned int index;
> > -       unsigned int parity;
> > -       unsigned char cw[8];
> > -    };
> > -
> > -
> >  Description
> >  -----------
> >
> > -.. note:: This ioctl is undocumented. Documentation is welcome.
> > -
> > +CA_SET_DESCR is used for feeding descrambler CA slots with descrambling
> > +keys (refered as control words).
> >
> >  Return Value
> >  ------------
> > diff --git a/include/uapi/linux/dvb/ca.h b/include/uapi/linux/dvb/ca.h
> > index f66ed53f4dc7..a62ddf0cebcd 100644
> > --- a/include/uapi/linux/dvb/ca.h
> > +++ b/include/uapi/linux/dvb/ca.h
> > @@ -109,9 +109,16 @@ struct ca_msg {
> >         unsigned char msg[256];
> >  };
> >
> > +/**
> > + * struct ca_descr - CA descrambler control words info
> > + *
> > + * @index: CA Descrambler slot
> > + * @parity: control words parity, where 0 means even and 1 means odd
> > + * @cw: CA Descrambler control words
> > + */
> >  struct ca_descr {
> >         unsigned int index;
> > -       unsigned int parity;    /* 0 == even, 1 == odd */
> > +       unsigned int parity;
> >         unsigned char cw[8];
> >  };
> >
> >  
> 
> Yeh, it should be that way.

Good! I'll add this patch to the series.

> BTW, the only issue I have in mind is how to link particular
> descrambler with the PID
> after your removal of the CA_SET_PID. And yes, I know that currently we have
> no any user of such ioctl in our driver base :)

Well, I don't think that an ioctl like CA_SET_PID would solve it.

On a generic case with is quite common nowadays on embedded hardware,
We have K demods and M CIs (where K may be different than M).

Also, You may need to route N PIDs to O descramblers.

As user switch channels, the N PIDs should be unset, and another
set of N' pids will be routed.

CA_SET_PID allows to set just one PID, without identifying from
what demod it would be received, and doesn't have a "reset" 
function to undo.

So, IMHO, the interface is broken by design. Perhaps that's
the reason why no upstream driver uses it.

What seems to be a much better design would be to use the demux
set filter ioctls and route the PIDs to the right CA.


Thanks,
Mauro

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[PATCH v2 00/26] Improve DVB documentation and reduce its gap Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:30 +0200
  [PATCH v2 11/27] media: fe_property_parameters.rst: better document bandwidth Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:40 +0200
  [PATCH v2 23/27] media: ca-get-slot-info.rst: document this ioctl Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:40 +0200
  [PATCH v2 18/27] media: ca.h: get rid of CA_SET_PID Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:40 +0200
  [PATCH v2 10/27] media: fe_property_parameters.rst: better define properties usage Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:40 +0200
  [PATCH v2 15/27] media: dmx.h: get rid of GET_DMX_EVENT Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:40 +0200
  [PATCH v2 12/27] media: dmx.h: get rid of unused DMX_KERNEL_CLIENT Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:40 +0200
  [PATCH v2 21/27] media: ca-reset.rst: add some description to this ioctl Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:40 +0200
  [PATCH v2 17/27] media: net.rst: Fix the level of a section of the net chapter Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:40 +0200
  [PATCH v2 03/27] media: dvb/intro: use the term Digital TV to refer to the system Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:50 +0200
  [PATCH v2 27/27] media: dst_ca: remove CA_SET_DESCR boilerplate Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-01 15:50 +0200
  Re: [PATCH v2 00/26] Improve DVB documentation and reduce its gap Honza Petrouš <jpetrous@gmail.com> - 2017-09-03 22:10 +0200
    Re: [PATCH v2 00/26] Improve DVB documentation and reduce its gap Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-04 03:00 +0200
      Re: [PATCH v2 00/26] Improve DVB documentation and reduce its gap Honza Petrouš <jpetrous@gmail.com> - 2017-09-04 09:20 +0200
        Re: [PATCH v2 00/26] Improve DVB documentation and reduce its gap Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-04 11:10 +0200
          Re: [PATCH v2 00/26] Improve DVB documentation and reduce its gap Honza Petrouš <jpetrous@gmail.com> - 2017-09-04 11:50 +0200
            Re: [PATCH v2 00/26] Improve DVB documentation and reduce its gap Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-04 13:50 +0200
    Re: [PATCH v2 00/26] Improve DVB documentation and reduce its gap Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-09-04 03:20 +0200
  Re: [PATCH v2 00/26] Improve DVB documentation and reduce its gap Honza Petrouš <jpetrous@gmail.com> - 2017-09-03 22:40 +0200

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