Re: [RFCv2 PATCH 4/6] videodev2.h: add frequency band information.

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 06/19/2012 02:47 AM, Mauro Carvalho Chehab wrote:
> Em 28-05-2012 07:46, Hans Verkuil escreveu:
>> From: Hans Verkuil <hans.verkuil@cisco.com>
>>
>> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
>> Acked-by: Hans de Goede <hdegoede@redhat.com>
>> ---
>>    include/linux/videodev2.h |   19 +++++++++++++++++--
>>    1 file changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
>> index 2339678..013ee46 100644
>> --- a/include/linux/videodev2.h
>> +++ b/include/linux/videodev2.h
>> @@ -2023,7 +2023,8 @@ struct v4l2_tuner {
>>    	__u32			audmode;
>>    	__s32			signal;
>>    	__s32			afc;
>> -	__u32			reserved[4];
>> +	__u32			band;
>> +	__u32			reserved[3];
>>    };
>>
>>    struct v4l2_modulator {
>> @@ -2033,7 +2034,8 @@ struct v4l2_modulator {
>>    	__u32			rangelow;
>>    	__u32			rangehigh;
>>    	__u32			txsubchans;
>> -	__u32			reserved[4];
>> +	__u32			band;
>> +	__u32			reserved[3];
>>    };
>>
>>    /*  Flags for the 'capability' field */
>> @@ -2048,6 +2050,11 @@ struct v4l2_modulator {
>>    #define V4L2_TUNER_CAP_RDS		0x0080
>>    #define V4L2_TUNER_CAP_RDS_BLOCK_IO	0x0100
>>    #define V4L2_TUNER_CAP_RDS_CONTROLS	0x0200
>> +#define V4L2_TUNER_CAP_BAND_FM_EUROPE_US     0x00010000
>> +#define V4L2_TUNER_CAP_BAND_FM_JAPAN         0x00020000
>> +#define V4L2_TUNER_CAP_BAND_FM_RUSSIAN       0x00040000
>> +#define V4L2_TUNER_CAP_BAND_FM_WEATHER       0x00080000
>> +#define V4L2_TUNER_CAP_BAND_AM_MW            0x00100000
>
> Frequency band is already specified by rangelow/rangehigh.
>
> Why do you need to duplicate this information?

Because radio tuners may support multiple non overlapping
bands, this is why this patch also adds a band member
to the tuner struct, which can be used to set/get
the current band.

One example of this are the tea5757 / tea5759
radio tuner chips:

FM:
tea5757 87.5 - 108 MHz
tea5759 76 - 91 MHz

AM:
Both: 530 - 1710 kHz

So an app would set as band one of DEFAULT, EUROPE_US
(or JAPAN depending on the model) and AM_MW, and then
get the actual range supported reported in rangelow /
rangehigh on a subsequent G_TUNER.

Note that setting ie a band of FM_JAPAN on a 5757 would
result in the S_TUNER failing with -EINVAL.

>
>
>>
>>    /*  Flags for the 'rxsubchans' field */
>>    #define V4L2_TUNER_SUB_MONO		0x0001
>> @@ -2065,6 +2072,14 @@ struct v4l2_modulator {
>>    #define V4L2_TUNER_MODE_LANG1		0x0003
>>    #define V4L2_TUNER_MODE_LANG1_LANG2	0x0004
>>
>> +/*  Values for the 'band' field */
>> +#define V4L2_TUNER_BAND_DEFAULT       0
>
> What does "default" mean?

Default means default. This is for compatibility with
old apps which don't know about the new tuner band API
extension so they will set this field to 0 (as reserved
fields should be set to 0 by userspace). In this case
we don't want to fail with -EINVAL based on the band
value, so we need some value all tuners will accept.

Some tuners, ie the si470x support both selecting a
specific FM band, as well as selecting a "universal"
FM band of 76 - 108 MHz. For those default would be
the universal FM band. For the tea575x devices discussed
above default would have the range of whatever FM band
they support.

Note that even on devices with a universal band being
able to select a certain band is quite useful to limit
hardware freq-seek to this band since searching freqs
below 87.5 is useless in europe / US for example.

Thinking more about this I think we should rename
V4L2_TUNER_BAND_DEFAULT to V4L2_TUNER_BAND_FM_UNIVERSAL,
and document that this means the widest FM band the
device supports, with the actual limits being reported
in rangelow and rangehigh. Note that the mentioned ranges
by the bands are indications of the expected range only
the true range will still be reported through rangelow and
rangehigh, and this is what apps are expected to use.

Defining 0 as V4L2_TUNER_BAND_FM_UNIVERSAL does cause
a -EINVAL when doing a S_TUNER with a band value of 0
on AM only tuners, but:
1) We don't support AM only tuners atm, and I don't expect
we will in the future either
2) Non band aware apps don't work well with AM tuners anyways
(as they must take much smaller frequency steps for one).

>
>> +#define V4L2_TUNER_BAND_FM_EUROPE_US  1       /* 87.5 Mhz - 108 MHz */
>
> EUROPE_US is a bad name for this range. According with Wikipedia, this
> range is used at "ITU region 1" (Europe/Africa), while America uses
> ITU region 2 (88-108).
>
> In Brazil, the range from 87.5-88 were added several years ago, so it is
> currently at the "ITU region 1" range, just like in US.
>
> I don't doubt that there are still some places at the 88-108 MHz range.

87.5 - 108 MHz is very close to 88 - 108 MHz, I don't think it is worth
creating 2 band defines for this.

>
>> +#define V4L2_TUNER_BAND_FM_JAPAN      2       /* 76 MHz - 90 MHz */
>
> This is currently true, but wikipedia points that they may increase it
> (from 76MHz to 108MHz?) after the end of NTSC broadcast.
>

This would be covered by the V4L2_TUNER_BAND_FM_UNIVERSAL, however,
on some devices V4L2_TUNER_BAND_FM_UNIVERSAL may include the weather band,
thus going all the way from 76 - 163 Mhz, so I guess we should add a
V4L2_TUNER_BAND_FM_JAPAN_WIDE for this. Note that the si470x already
supports this, and indeed calls it "Japan wide band"

> The DTV range there starts at channel 14 (473 MHz and upper). Maybe they
> may reserve the channel 7-13 range (VHF High - starting at 177 MHz) like
> Brazil for DTV.
>
> Anyway, what I mean is that calling a frequency range with a Country name
> is dangerous, as frequency ranges can vary from time to time.
>

So lets get back to the basis, for AM/FM switching / limiting hw-freq
seeking, and on some devices likely even just to be able to tune to
certain frequencies we need to select a band with various radio devices.

On some radio devices we may be able to just program the seek range, but on
most it is hardcoded based on a band selection register.

So we need some way of naming the bands, with approx. expected ranges
(the real range supported by the specific device will be reported on a
G_TUNER).

Looking at:
http://en.wikipedia.org/wiki/FM_broadcast_band

I suggest naming the bands after their standards, except for the Japanese
bands which are special and I suggest just naming them after their
country, resulting in:

#define V4L2_TUNER_BAND_FM_CCIR		1 /* 87.5 - 108 Mhz */
#define V4L2_TUNER_BAND_FM_OIRT		2 /* 65.8 MHz - 74 MHz */
#define V4L2_TUNER_BAND_JAPAN		3 /* 76 MHz - 90 MHz */
#define V4L2_TUNER_BAND_JAPAN_WIDE	4 /* 76 MHz - 108 MHz */
#define V4L2_TUNER_BAND_WEATHER		5 /* 162.4 MHz - 162.55 MHz */

Note for rationale of the weather band, see:
http://en.wikipedia.org/wiki/Weather_radio

Regards,

Hans