Re: [Linux-kernel-mentees] [v10 0/4] media: vidtv: Implement a virtual DVB driver

From: "Daniel W. S. Almeida" <dwlsalmeida@gmail.com>
To: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: "r.verdejo@samsung.com" <r.verdejo@samsung.com>,
	"linux-media@vger.kernel.org\"        
	<linux-media@vger.kernel.org>,
	skhan@linuxfoundation.org <skhan@linuxfoundation.org>,
	linux-kernel-mentees@lists.linuxfoundation.org\""
	<linux-kernel-mentees@lists.linuxfoundation.org>,
	"linux-kernel@vger.kernel.org\"" <linux-kernel@vger.kernel.org>,
	"nicolas@ndufresne.ca" <nicolas@ndufresne.ca>
Subject: Re: [Linux-kernel-mentees] [v10 0/4] media: vidtv: Implement a virtual DVB driver
Date: Fri, 11 Sep 2020 23:54:15 -0300	[thread overview]
Message-ID: <78C65222-868B-404B-974E-D8808586845A@getmailspring.com> (raw)
In-Reply-To: <20200911155640.79a15a14@coco.lan>

Hi Mauro,

> Ok, I guess I got what should be done here. ETSI TS 102 154 says that
> SMPTE 302M should use the "registration_descriptor".
> 
> From the specs, such descriptor should be filled with 
> format_identifier = 0x42535344.
> 
> We need to add this on both at v4l-utils and at the vidtv driver.

vidtv will already attach a registration descriptor for s302m audio, i.e.

dvb_parse_section: table 0x02, extension ID 0x0880: done
PMT
| table_id 0x02
| section_length 24
| one 2
| zero 0
| syntax 1
| transport_stream_id 2176
| current_next 1
| version 1
| one2 3
| section_number 0
| last_section_number 0
|- pcr_pid 0200
| reserved2 7
| descriptor length 0
| zero3 0
| reserved3 15
|\
|- stream 0x0111: ISO/IEC 13818-1 Private Data (6)
| descriptor length 6
| 0x05: registration_descriptor
| 42 53 53 44 BSSD <<<<<<<<<<< here it is
|_ 1 streams

So I guess I need to add support for it on v4l-utils then? Any tips on
how to get started?

By the way,

> My plan is to write some patches on the top of yours, in order to
> address the problems I'll find on it. If not something more critical
> won't be solved in time, we may still add it at staging/media. 
> Let's see.

Can you teach me how this works in git? Am I supposed to cherry-pick
your patches, or apply & rebase -i & squash, or something else?

>Well, if you have some spare time, you could try to write
>a debugfs binding for vidtv. The best would be to have it
>on a separate file. Failing to bind debugfs should not
>prevent loading the bridge driver.

Sure, can you provide more details on how this and vidtv should play
together? I will catch up on
the documentation for debugfs in the meantime

As for vidtv_s302m_write_frame:

>doing that didn't work. Yet, this check inside the driver:

What didn't work? It didn't compile? I should have sent a proper diff
but I was short on time, sorry...

-- thanks
-- Daniel
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