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Date:   Mon, 9 Jul 2018 10:59:38 -0300
From:   Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
To:     "Katsuhiro Suzuki" <suzuki.katsuhiro@socionext.com>
Cc:     <linux-media@vger.kernel.org>,
        "Masami Hiramatsu" <masami.hiramatsu@linaro.org>,
        "Jassi Brar" <jaswinder.singh@linaro.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, "Abylay Ospan" <aospan@netup.ru>
Subject: Re: [PATCH v3] media: dvb-frontends: add Socionext SC1501A ISDB-S/T
 demodulator driver
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Em Mon, 9 Jul 2018 11:04:36 +0900
"Katsuhiro Suzuki" <suzuki.katsuhiro@socionext.com> escreveu:

> Hello Mauro,
>=20
> > -----Original Message-----
> > From: linux-media-owner@vger.kernel.org <linux-media-owner@vger.kernel.=
org> On
> > Behalf Of Mauro Carvalho Chehab
> > Sent: Friday, July 6, 2018 8:16 PM
> > To: Suzuki, Katsuhiro/=E9=88=B4=E6=9C=A8 =E5=8B=9D=E5=8D=9A <suzuki.kat=
suhiro@socionext.com>
> > Cc: linux-media@vger.kernel.org; Masami Hiramatsu =20
> <masami.hiramatsu@linaro.org>;
> > Jassi Brar <jaswinder.singh@linaro.org>; linux-arm-kernel@lists.infrade=
ad.org;
> > linux-kernel@vger.kernel.org; Abylay Ospan <aospan@netup.ru>
> > Subject: Re: [PATCH v3] media: dvb-frontends: add Socionext SC1501A ISD=
B-S/T
> > demodulator driver
> >=20
> > Em Fri, 6 Jul 2018 15:04:08 +0900
> > "Katsuhiro Suzuki" <suzuki.katsuhiro@socionext.com> escreveu:
> >  =20
> > > Here is the log of dvb-fe-tool on my environment.
> > >
> > > --------------------
> > > # ./utils/dvb/.libs/dvb-fe-tool -d isdbs
> > > Changing delivery system to: ISDBS
> > > ERROR    FE_SET_VOLTAGE: Unknown error 524 =20
> >=20
> > Hmm... ENOTSUPP. Doesn't the device supposed to be able to power on the
> > LNBf? =20
>=20
> Ah, maybe it's not implemented yet in Helene driver.

That depends on how the hardware works. On some hardware, the
LNBf power supply and control is at the demod; on others, it is=20
supported by a separate chipset. See, for example, isl642.c for
an example of such external hardware.

I don't know much about ISDB-S, but, as far as what was
implemented on v4l-utils dvb-sat.c for Japan 110BS/CS LNBf,
the LNBf voltage is not used to switch the polarity.

So, the control here is simpler than on DVB-S/S2, as the only
control is either to send 18V to power on the LNBf/Dish, or
zero in order to save power.

>=20
>=20
> >=20
> > Anyway, I changed the error print message to be clearer, displaying
> > instead:
> >=20
> >   ERROR    FE_SET_VOLTAGE: driver doesn't support it!
> >  =20
>=20
> It's nice for users. Thanks!
>=20
>=20
> > >
> > > # ./utils/dvb/.libs/dvb-fe-tool
> > > Device Socionext SC1501A (/dev/dvb/adapter0/frontend0) capabilities:
> > >      CAN_FEC_AUTO
> > >      CAN_GUARD_INTERVAL_AUTO
> > >      CAN_HIERARCHY_AUTO
> > >      CAN_INVERSION_AUTO
> > >      CAN_QAM_AUTO
> > >      CAN_TRANSMISSION_MODE_AUTO
> > > DVB API Version 5.11, Current v5 delivery system: ISDBS
> > > Supported delivery systems:
> > >     [ISDBS]
> > >      ISDBT
> > > Frequency range for the current standard:
> > > From:             470 MHz
> > > To:              2.07 GHz
> > > Step:            25.0 kHz
> > > Symbol rate ranges for the current standard:
> > > From:                 0Bauds
> > > To:                   0Bauds =20
> >=20
> > That seems a driver issue. The ISDB-S ops.info should be
> > filling both symbol_rate_min and symbol_rate_max.
> >=20
> > I suspect that both should be filled with 28860000.
> >=20
> > The dvb_frontend.c core might hardcode it, but, IMHO,
> > it is better to keep those information inside the
> > tuner/frontend ops.info.
> >  =20
>=20
> Indeed, thank you for reviewing. I fixed my driver. It seems works fine.
>=20
> ----
> # utils/dvb/.libs/dvb-fe-tool -a 0
> Device Socionext SC1501A (/dev/dvb/adapter0/frontend0) capabilities:
>      CAN_FEC_AUTO
>      CAN_GUARD_INTERVAL_AUTO
>      CAN_HIERARCHY_AUTO
>      CAN_INVERSION_AUTO
>      CAN_QAM_AUTO
>      CAN_TRANSMISSION_MODE_AUTO
> DVB API Version 5.11, Current v5 delivery system: ISDBS
> Supported delivery systems:
>     [ISDBS]
>      ISDBT
> Frequency range for the current standard:
> From:             470 MHz
> To:              2.07 GHz
> Step:            25.0 kHz
> Symbol rate ranges for the current standard:
> From:            28.9 MBauds
> To:              28.9 MBauds
> SEC: set voltage to OFF
> ERROR    FE_SET_VOLTAGE: Operation not permitted
> ----

That sounds ok.

>=20
>=20
> > > SEC: set voltage to OFF
> > > ERROR    FE_SET_VOLTAGE: Operation not permitted
> > >
> > >
> > > # ./utils/dvb/.libs/dvb-fe-tool -d isdbt
> > > Changing delivery system to: ISDBT
> > > ERROR    FE_SET_VOLTAGE: Unknown error 524
> > >
> > > # ./utils/dvb/.libs/dvb-fe-tool
> > > Device Socionext SC1501A (/dev/dvb/adapter0/frontend0) capabilities:
> > >      CAN_FEC_AUTO
> > >      CAN_GUARD_INTERVAL_AUTO
> > >      CAN_HIERARCHY_AUTO
> > >      CAN_INVERSION_AUTO
> > >      CAN_QAM_AUTO
> > >      CAN_TRANSMISSION_MODE_AUTO
> > > DVB API Version 5.11, Current v5 delivery system: ISDBT
> > > Supported delivery systems:
> > >      ISDBS
> > >     [ISDBT]
> > > Frequency range for the current standard:
> > > From:             470 MHz
> > > To:              2.07 GHz
> > > Step:            25.0 kHz =20
> >=20
> > The rest looks OK for me.
> >  =20
> > > > > For example, Helene uses these info for only Ter or Sat freq rang=
es:
> > > > >
> > > > > 		.name =3D "Sony HELENE Ter tuner",
> > > > > 		.frequency_min_hz  =3D    1 * MHz,
> > > > > 		.frequency_max_hz  =3D 1200 * MHz,
> > > > > 		.frequency_step_hz =3D   25 * kHz,
> > > > >
> > > > > 		.name =3D "Sony HELENE Sat tuner",
> > > > > 		.frequency_min_hz  =3D  500 * MHz,
> > > > > 		.frequency_max_hz  =3D 2500 * MHz,
> > > > > 		.frequency_step_hz =3D    1 * MHz,
> > > > >
> > > > > Is this better to add new info for both system?
> > > > >
> > > > > 		.name =3D "Sony HELENE Sat/Ter tuner",
> > > > > 		.frequency_min_hz  =3D    1 * MHz,
> > > > > 		.frequency_max_hz  =3D 2500 * MHz,
> > > > > 		.frequency_step_hz =3D   25 * kHz, // Is this correct...? =20
> > > >
> > > > That is indeed a very good question, and maybe a reason why we
> > > > may need other approaches.
> > > >
> > > > See, if the tuner is capable of tuning from 1 MHz to 2500 MHz,
> > > > the frequency range should be ok. It would aget_frontend_algoctuall=
y be =20
> pretty
> > cool =20
> > > > to use a tuner with such wide range for SDR, if the hardware suppor=
ts
> > > > raw I/Q collect :-D
> > > >
> > > > The frequency step is a different issue. If the tuner driver uses
> > > > DVBFE_ALGO_SW (e. g. if ops.get_frontend_algo() returns it, or if
> > > > this function is not defined), then the step will be used to adjust
> > > > the zigzag interactions. If it is too small, the tuning will lose
> > > > channels if the signal is not strong.
> > > > =20
> > >
> > > Thank you for describing. It's difficult problem... =20
> >=20
> > I double-checked the implementation. We don't need to worry about
> > zigzag, provided that the ISDB-S implementation at the core is correct.
> >=20
> > For satellite/cable standards, the zigzag logic takes the symbol
> > rate into account, and not the stepsize:
> >=20
> >                 case SYS_DVBS:
> >                 case SYS_DVBS2:
> >                 case SYS_ISDBS:
> >                 case SYS_TURBO:
> >                 case SYS_DVBC_ANNEX_A:
> >                 case SYS_DVBC_ANNEX_C:
> >                         fepriv->min_delay =3D HZ / 20;
> >                         fepriv->step_size =3D c->symbol_rate / 16000;
> >                         fepriv->max_drift =3D c->symbol_rate / 2000;
> >                         break;
> >=20
> > For terrestrial standards, it uses the stepsize:
> >=20
> >                 case SYS_DVBT:
> >                 case SYS_DVBT2:
> >                 case SYS_ISDBT:
> >                 case SYS_DTMB:
> >                         fepriv->min_delay =3D HZ / 20;
> >                         fepriv->step_size =3D dvb_frontend_get_stepsize=
(fe) * 2;
> >                         fepriv->max_drift =3D (dvb_frontend_get_stepsiz=
e(fe) * 2) =20
> +
> > 1;
> >                         break;
> >=20
> > So, having a value of 25 kHz there won't affect the zigzag algorithm
> > for ISDB-S, as it will be used only for ISDB-T.
> >  =20
>=20
> Thank you for checking and describing. I checked it too.
>=20
> Default value is fine as you said, and we can use get_tune_settings()=20
> callback if we face the problem or need different settings for each=20
> delivery systems in the future.
>=20
>         /* get frontend-specific tuning settings */
>         memset(&fetunesettings, 0, sizeof(struct dvb_frontend_tune_settin=
gs));
>         if (fe->ops.get_tune_settings && (fe->ops.get_tune_settings(fe,
> &fetunesettings) =3D=3D 0)) {
>                 fepriv->min_delay =3D (fetunesettings.min_delay_ms * HZ) =
/ 1000;
>                 fepriv->max_drift =3D fetunesettings.max_drift;
>                 fepriv->step_size =3D fetunesettings.step_size;
>         } else {
>                 /* default values */
>                 ...

Sure.=20

>=20
>=20
> > > > In the specific case of helene, it doesn't have a get_frontend_algo,
> > > > so it will use the step frequency.
> > > >
> > > > I'm not sure how to solve this issue. Maybe Abylay may shed a light
> > > > here, if helene does sigzag in hardware or not.
> > > > =20
> > >
> > > As far as I know, Helene does not have automatic scan mechanism in
> > > hardware. =20
> >=20
> > Ok, so the driver is doing the right thing here.
> >  =20
> > > > If it does in hardware, you could add a get_frontend_algo() routine
> > > > at helene driver and return DVBFE_ALGO_HW. The tuning zigzag softwa=
re
> > > > algorithm in the Kernel will stop, as it will rely at the hardware.
> > > >
> > > > Please notice that, if the hardware doesn't do zigzag itself, this
> > > > will make it lose channels. On the other hand, if the hardware does
> > > > have sigzag, changing to DVBFE_ALGO_HW will speedup tuning, as the
> > > > Kernel won't try to do sigzag itself.
> > > > =20
> > >
> > > ISDB-T uses 6MHz bandwidth per channel (in Japan), ISDB-S for
> > > BS/CS110 uses 38.36MHz bandwidth. Maybe 1MHz zigzag step is large for
> > > ISDB-T system and 25kHz is small for ISDB-S system. =20
> >=20
> > Yeah, but, after double-checking the logic, for ISDB-S, it will
> > use:
> >=20
> > 	c->symbol_rate =3D 28860000;
> > 	c->rolloff =3D ROLLOFF_35;
> > 	c->bandwidth_hz =3D c->symbol_rate / 100 * 135;
> >=20
> > That would actually set the ISDB-S channel separation to 38.961 MHz.
> >=20
> > By setting symbol_rate like that, the zigzag for ISDB-S will
> > be defined by:
> >=20
> >        fepriv->step_size =3D c->symbol_rate / 16000; /* 38.961MHz / 160=
00 =3D =20
> .002435
> > - e. g. steps of ~25 kHz */
> >        fepriv->max_drift =3D c->symbol_rate / 2000;  /* 38.961MHz / 200=
0 =3D =20
> .0194805
> > - e. g. max drift of ~195 kHz */
> >=20
> > Funny enough, it will be using about 25 kHz as step size for ISDB-S.
> >=20
> > I have no idea if the ISDB-S standard defines the zigzag logic,
> > but I would be expecting a higher value for it. So, perhaps
> > the ISDB-S zigzag could be optimized.
> >=20
> > Thanks,
> > Mauro =20
>=20
> Hmm, interesting. I don't know zigzag for ISDB-S too, sorry...
>=20
> Anyway, I don't worry about that. I said in above, we can use=20
> get_tune_settings() for fine tuning.
>=20
>=20
> Regards,
> --
> Katsuhiro Suzuki
>=20
>=20
>=20


Thanks,
Mauro