Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753548AbdIDJlD (ORCPT ); Mon, 4 Sep 2017 05:41:03 -0400 Received: from mail-qk0-f196.google.com ([209.85.220.196]:36242 "EHLO mail-qk0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753390AbdIDJlA (ORCPT ); Mon, 4 Sep 2017 05:41:00 -0400 X-Google-Smtp-Source: ADKCNb6Sm3F2elbGuIkceKglqp8Ar9AS6+XY/8WYDVGkHye74HuLRzxdPoPScCzcaaaUCJRlkZJjEK5ENICDS5n9mqo= MIME-Version: 1.0 In-Reply-To: <20170904060629.2f8feeab@vento.lan> References: <20170903215404.425af4aa@vento.lan> <20170904060629.2f8feeab@vento.lan> From: =?UTF-8?Q?Honza_Petrou=C5=A1?= Date: Mon, 4 Sep 2017 11:40:59 +0200 Message-ID: Subject: Re: [PATCH v2 00/26] Improve DVB documentation and reduce its gap To: Mauro Carvalho Chehab Cc: Linux Doc Mailing List , Linux Media Mailing List , Mauro Carvalho Chehab , linux-kernel@vger.kernel.org, Jonathan Corbet Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v849f662031188 Content-Length: 5712 Lines: 168 2017-09-04 11:06 GMT+02:00 Mauro Carvalho Chehab : > Em Mon, 4 Sep 2017 09:12:49 +0200 > Honza Petrouš escreveu: > >> 2017-09-04 2:54 GMT+02:00 Mauro Carvalho Chehab : >> > Em Sun, 3 Sep 2017 22:05:23 +0200 >> > Honza Petrouš 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 >> > Signed-off-by: Mauro Carvalho Chehab >> > >> > 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. TBH that is exactly most common use-case = most Digital TV vendors are scrambling per-service, what requires one descrambler for all scrambled PIDs (usually only A/V PIDs are scrambled) for particular service. So we have to add more PIDs to one descrambler What was possible by multiple call of CA_SET_PID (I agree that much better would be name like CA_ADD_PID) > > 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. Here I can agree - it looks like the value -1 in 'index' should do the job, but it, unfortunately, looses info from which descrambler it should be removed (see note in struct ca_pid for value -1) > > So, IMHO, the interface is broken by design. Perhaps that's > the reason why no upstream driver uses it. I have the same feeling regarding brokenness. > > 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. > I don't have access to any programmer reference documentation for any modern DVB-enabled SoC, but I see two possible scenario of connecting descramblers to the demuxes (most of modern SoCs have more then one demux) - static one, when every demux has predefined descramblers already connected to it and dynamic ones, when any descrambler can be connected to the any demux. >From that reason I vote to have some descrambler specific ioctl, which allow more flexibility then if we add it to the filter set ioctl. My 5 cents /Honza PS: I understand that until we get some multi-descrambler device included, we don't need to address descrambler management.