On 12.03.2014 15:21, Mauro Carvalho Chehab wrote:
Em Wed, 12 Mar 2014 15:07:02 +0200
Antti Palosaari <crope@xxxxxx> escreveu:
On 12.03.2014 14:57, Antti Palosaari wrote:
On 12.03.2014 14:47, Mauro Carvalho Chehab wrote:
Em Wed, 12 Mar 2014 14:26:35 +0200
Antti Palosaari <crope@xxxxxx> escreveu:
On 12.03.2014 13:02, Mauro Carvalho Chehab wrote:
Em Mon, 10 Mar 2014 12:01:28 +0200
Antti Palosaari <crope@xxxxxx> escreveu:
On 05.03.2014 20:49, Mauro Carvalho Chehab wrote:
Em Thu, 27 Feb 2014 02:22:06 +0200
Antti Palosaari <crope@xxxxxx> escreveu:
Add documentation for RF tuner bandwidth controls. These controls
are
used to set filters on tuner signal path.
Cc: Hans Verkuil <hverkuil@xxxxxxxxx>
Signed-off-by: Antti Palosaari <crope@xxxxxx>
---
Documentation/DocBook/media/v4l/controls.xml | 19
+++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/Documentation/DocBook/media/v4l/controls.xml
b/Documentation/DocBook/media/v4l/controls.xml
index 6c9dbf6..5550fea 100644
--- a/Documentation/DocBook/media/v4l/controls.xml
+++ b/Documentation/DocBook/media/v4l/controls.xml
@@ -5007,6 +5007,25 @@ descriptor. Calling &VIDIOC-QUERYCTRL; for
this control will return a
description of this control class.</entry>
</row>
<row>
+ <entry
spanname="id"><constant>V4L2_CID_RF_TUNER_BANDWIDTH_AUTO</constant> </entry>
+ <entry>boolean</entry>
+ </row>
+ <row>
+ <entry spanname="descr">Enables/disables tuner
radio channel
+bandwidth configuration. In automatic mode bandwidth
configuration is performed
+by the driver.</entry>
+ </row>
+ <row>
+ <entry
spanname="id"><constant>V4L2_CID_RF_TUNER_BANDWIDTH</constant> </entry>
+ <entry>integer</entry>
+ </row>
+ <row>
+ <entry spanname="descr">Filter(s) on tuner signal
path are used to
+filter signal according to receiving party needs. Driver
configures filters to
+fulfill desired bandwidth requirement. Used when
V4L2_CID_RF_TUNER_BANDWIDTH_AUTO is not
+set. The range and step are driver-specific.</entry>
Huh? If this is enable/disable, why "the range and step are
driver-specific"?
Because there is two controls grouped. That is situation of having
AUTO/MANUAL.
V4L2_CID_RF_TUNER_BANDWIDTH_AUTO
V4L2_CID_RF_TUNER_BANDWIDTH
V4L2_CID_RF_TUNER_BANDWIDTH is valid only when
V4L2_CID_RF_TUNER_BANDWIDTH_AUTO == false.
Sorry, but I'm not understanding what you're arguing.
Yeah, it is clear at the patch that there are two controls, and that
V4L2_CID_RF_TUNER_BANDWIDTH is valid only when AUTO is disabled, but
this doesn't answer my question:
Why V4L2_CID_RF_TUNER_BANDWIDTH's range and step are driver-specific?
Hmmm. That control is used to configure RF filters. Filters set
bandwidth of radio channel. There is usually quite limited set of
available analog filters inside RF tuner. If you look for example
FC0012/FC0013 possible filters are 6/7/8 MHz. E4000 has something 4-11
MHz. If you look those very old 1st gen silicon tuners like QT1010 /
MT2060, there is no integrated filters at all - but there is external
saw filter which is usually 8MHz at 36.125 MHz IF.
Did you remember there is same parameter already in DVB API (struct
dtv_frontend_properties bandwidth_hz)? That is control is currently used
to set r820t, fc0012, fc10013 .bandwidth_hz value, e4000 implements it
correctly as own control.
I am quite astonished we have that big gap with our views.
Well, on DVB, the bandwidth is specified in Hz, at DVBv5 (or via
an enum on DVBv3).
Here, there's no description about the unit to be used (Hz? kHz?).
It just says that this is an integer, with a driver-specific
range and step.
So, one driver might choose to use Hz, other kHz, and other to
expose some internal counter. That's bad.
We should either use a V4L2_CTRL_TYPE_MENU type of control, where it
would be possible to do something similar to DVBv3 way to specify
the bandwidth filter, or to define that the bandwidth will be
in Hz, kHz or MHz.
Yeah, indeed. That was my mistake. The aim was Hz yes.
Probably, a menu type is better, as it allows userspace to get
all supported bandwidths.
I though it too, but there is already a lot choices for some tuners,
E4000 has over 30. What is maximum reasonable filter count for
V4L2_CTRL_TYPE_MENU?
I don't see any troubles on having 30 items there. Maybe Hans is aware
of some troubles on having such number of items.
The advantage of a menu type is that it helps userspace to select
an existing range.
One fear there is also what happens when there will be some day new RF
tuner having DSP which does digital filtering ~1 Hz step?
It is possible.
Mabbe the current control is enough, but probably it is place to add
comment unit is Hz (even I think people should expect it is Hz when RF
frequencies are spoken).
Please remind that V4L2 API has 3 scales already for frequencies,
HZ being the less obvious one, as it is the one added only for
3.14 and upper.
I see two alternatives here:
1) say that this is always Hz. The problem is if some future hardware
would support a bandwidth bigger than 2 GHz. That's unlikely, as
using such filter would require a wide band antenna, but
I won't doubt that this might happen some day;
Antenna dimensions are relative. 2GHz is not so much when we speak
frequencies over 100 GHz and so. But it is very far away from the
environment we are now playing with...
2) say that this should follow the corresponding tuner CAPS for
frequencies (V4L2_TUNER_CAP_LOW, V4L2_TUNER_CAP_NORM, V4L2_TUNER_CAP_1HZ).
The advantage of (2) is that, if we latter need to support wide band
filters, one would just need to use V4L2_TUNER_CAP_NORM (or a newer
V4L2_TUNER_CAP_1KHZ).
That is fine for me too, but I suspect Hans don't like it, as those
steps are mapped "V4L tuner API", right?
Anyway, is that something we can just put in and fine tune later if
needed? I cannot see big issues and it is still experimental and all
drivers are staging....
regards
Antti
--
http://palosaari.fi/
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