On 09/28/2012 08:07 PM, Hans Verkuil wrote:
On Fri September 28 2012 17:30:05 Mauro Carvalho Chehab wrote:
Em Fri, 28 Sep 2012 16:21:35 +0200
Hans Verkuil <hverkuil@xxxxxxxxx> escreveu:
On Fri September 28 2012 14:43:32 Hans Verkuil wrote:
Hi Antti,
Mauro asked me to look into LNA as well, in particular how this could be done
on the analog side as well.
Thanks for that!
While reading through this patch I noticed that the new property was added to
dtv_property_process_set, but not to dtv_property_process_get. Can you look
into that and add 'get' support for this property?
It's a sign of insanity when you start replying to your own email, but so
be it :-)
:)
I've been thinking how this can be implemented in such a way that it works
well in all the various board/tuner configurations.
First, the property should be cached in dtv_frontend_properties, that way
tuners with a built-in LNA can use it. The initial value should be AUTO,
I guess.
The property_process_set code changes to:
case DTV_LNA:
if (fe->ops.set_lna)
r = fe->ops.set_lna(fe, tvp->u.data);
if (!r)
c->lna = tvp->u.data;
break;
Tuners can now check the c->lna value when set_params is called and take the
appropriate steps if they have a built-in LNA.
To be able to access the LNA from the V4L2 side you would need to add two
new tuner ops in include/media/v4l2-subdev.h:
int (*g_lna)(struct v4l2_subdev *sd, u32 *lna);
int (*s_lna)(struct v4l2_subdev *sd, u32 lna);
The tuner-core.c driver can implement these ops to get and set c->lna accordingly.
A menu control would be needed to actually change the LNA.
The code that handles that control would have to call a board-specific function
if necessary (if the LNA is on the board), and call the tuner's s_lna op otherwise.
Makes sense.
The only question is whether the digital and analog APIs should share the same
LNA setting or keep different LNA states for each.
So if I call DTV_LNA to set the LNA, and then check the LNA control value from V4L2,
should the two match? Or should we keep separate states and whenever you select
digital or analog mode the LNA is updated with the corresponding LNA value for that
mode.
The latter is a bit more work (struct analog_parameters should probably be extended
with an LNA value), but I do think it is a cleaner solution.
I think they both should share the same LNA state, as this depends on the physical
connection (e. g. if the antenna has LNA; if the signal reception is weak or strong
with that particular antenna).
I am not sure if the LNA work on the analog side should be done without having
hardware that actually uses it, but at least the LNA support on the digital side
should be done in such a way that it can be extended for analog as well.
There are several saa7134 hardware with LNA support. I have one of such boards
here, although never needed to dig into the LNA stuff on it.
I'll wait until Antti makes the necessary changes on the digital side, after that
I'll see if I can make a patch for the analog part, and post that. There is an
outside chance that I have a board with an LNA as well: for ivtv there were issues
with a Samsung TCPN 2121P30A tuner where the LNA had to be turned on or off manually
(it should have been automatic but due to a hardware bug that didn't work). This
was never supported in ivtv, but this would make a good test case.
The only problem is that I don't know if I still have that card or if I gave it
to Andy. I think it went to him, actually.
Hans, your changes moving lna to property cache is fine for my eyes. I
can change it if you wish, but maybe Sunday or next week
I dropped get operation originally as I wanted to keep workload small on
that time. Also there was some other design issues, like one I selected
AUTO as minimum possible value to leave space for extending possible
values (both attenuation and gain). For now it is just on/off, but there
is existing LNAs having more gain levels, not to mention VGAs and LNAs
integrated to RF-tuners. Other design issue was units. Gains are
measured as units of decibels, but I decided to use device specific
steps instead of making some mechanism to enumerate supported gain levels.
Here is some discussion behind that LNA.
http://www.spinics.net/lists/linux-media/msg50132.html
http://www.spinics.net/lists/linux-media/msg50133.html
http://www.spinics.net/lists/linux-media/msg50139.html
http://blog.palosaari.fi/2012/07/patch-rfc-add-lna-support-for-dvb-api.html
regards
Antti
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http://palosaari.fi/
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