linux-kernel - Re: stable regression: tda18271_read_regs: [1-0060|M] ERROR: i2c

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Message-ID: <52B0BD72.9000804@iki.fi>
Date:	Tue, 17 Dec 2013 23:09:06 +0200
From:	Antti Palosaari <crope@....fi>
To:	Devin Heitmueller <dheitmueller@...nellabs.com>,
	Connor Behan <connor.behan@...il.com>
CC:	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Frederik Himpe <fhimpe@...enet.be>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Media Mailing List <linux-media@...r.kernel.org>
Subject: Re: stable regression: tda18271_read_regs: [1-0060|M] ERROR: i2c_transfer
 returned: -19

Off-topic, Cc:s dropped, related to DVB / V4L2 tuner communication problems.

On 17.12.2013 07:39, Devin Heitmueller wrote:
> Hi Connor,
>
> On Tue, Dec 17, 2013 at 12:28 AM, Connor Behan <connor.behan@...il.com> wrote:
>> Thanks for the detailed answer. I have tried your patch and updated the
>> wiki page. Would a 950 or 950Q be safer to buy next time?
>
> The 950 has long since been obsoleted.  You cannot buy them anymore.
> The 950q though is well supported and doesn't have this issue as it
> uses a different chip.
>
>> On 14/12/13 05:17 PM, Devin Heitmueller wrote:
>>> I had a patch kicking around which fixed part of the issue, but it
>>> didn't completely work because of the lgdt3305 having AGC enabled at
>>> chip powerup (which interferes with analog tuning on the shared
>>> tuner), and the internal v4l-dvb APIs don't provide any easy way to
>>> reset the AGC from the analog side of the device.
>>
>> By this do you mean that the functions exist but they aren't part of the
>> public API? Maybe this problem can be addressed if there is ever "v4l3"
>> or some other reason to break compatibility.
>
> No, these are internal APIs that dictate how the various driver
> components talk to each other.  Because the V4L and DVB subsystems
> were developed independently of each other, they do a really crappy
> job of communicating between them (a problem which manifests itself in
> particular when sharing hardware resources such as tuners).
>
> The problem *can* be fixed, but it would likely require
> extensions/changes to the basic frameworks used to communicate between
> the different drivers.

That shared DVB / V4L2 tuner is one problem that I have also currently 
(SDR is on V4L2 API and DTV is provided via DVB API). I have decided to 
try model where I separate RF tuner totally independent used DVB / V4L2 
APIs, just to plain I2C driver model. Idea is here to provide needed set 
of general callbacks and communication and device binding is done via 
I2C driver model.
I am not sure though if there is any big caveats I haven't realized yet...

regards
Antti

-- 
http://palosaari.fi/
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