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SubjectRe: [PATCH v3] media: dvb-frontends: add Socionext SC1501A ISDB-S/T demodulator driver
Date
Hello Mauro,

> -----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/鈴木 勝博 <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
>
> Em Fri, 6 Jul 2018 15:04:08 +0900
> "Katsuhiro Suzuki" <suzuki.katsuhiro@socionext.com> escreveu:
>
> > 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
>
> Hmm... ENOTSUPP. Doesn't the device supposed to be able to power on the
> LNBf?

Ah, maybe it's not implemented yet in Helene driver.


>
> Anyway, I changed the error print message to be clearer, displaying
> instead:
>
> ERROR FE_SET_VOLTAGE: driver doesn't support it!
>

It's nice for users. Thanks!


> >
> > # ./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
>
> That seems a driver issue. The ISDB-S ops.info should be
> filling both symbol_rate_min and symbol_rate_max.
>
> I suspect that both should be filled with 28860000.
>
> The dvb_frontend.c core might hardcode it, but, IMHO,
> it is better to keep those information inside the
> tuner/frontend ops.info.
>

Indeed, thank you for reviewing. I fixed my driver. It seems works fine.

----
# 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
----


> > 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
>
> The rest looks OK for me.
>
> > > > For example, Helene uses these info for only Ter or Sat freq ranges:
> > > >
> > > > .name = "Sony HELENE Ter tuner",
> > > > .frequency_min_hz = 1 * MHz,
> > > > .frequency_max_hz = 1200 * MHz,
> > > > .frequency_step_hz = 25 * kHz,
> > > >
> > > > .name = "Sony HELENE Sat tuner",
> > > > .frequency_min_hz = 500 * MHz,
> > > > .frequency_max_hz = 2500 * MHz,
> > > > .frequency_step_hz = 1 * MHz,
> > > >
> > > > Is this better to add new info for both system?
> > > >
> > > > .name = "Sony HELENE Sat/Ter tuner",
> > > > .frequency_min_hz = 1 * MHz,
> > > > .frequency_max_hz = 2500 * MHz,
> > > > .frequency_step_hz = 25 * kHz, // Is this correct...?
> > >
> > > 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_algoctually be
pretty
> cool
> > > to use a tuner with such wide range for SDR, if the hardware supports
> > > 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.
> > >
> >
> > Thank you for describing. It's difficult problem...
>
> I double-checked the implementation. We don't need to worry about
> zigzag, provided that the ISDB-S implementation at the core is correct.
>
> For satellite/cable standards, the zigzag logic takes the symbol
> rate into account, and not the stepsize:
>
> 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 = HZ / 20;
> fepriv->step_size = c->symbol_rate / 16000;
> fepriv->max_drift = c->symbol_rate / 2000;
> break;
>
> For terrestrial standards, it uses the stepsize:
>
> case SYS_DVBT:
> case SYS_DVBT2:
> case SYS_ISDBT:
> case SYS_DTMB:
> fepriv->min_delay = HZ / 20;
> fepriv->step_size = dvb_frontend_get_stepsize(fe) * 2;
> fepriv->max_drift = (dvb_frontend_get_stepsize(fe) * 2)
+
> 1;
> break;
>
> 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.
>

Thank you for checking and describing. I checked it too.

Default value is fine as you said, and we can use get_tune_settings()
callback if we face the problem or need different settings for each
delivery systems in the future.

/* get frontend-specific tuning settings */
memset(&fetunesettings, 0, sizeof(struct dvb_frontend_tune_settings));
if (fe->ops.get_tune_settings && (fe->ops.get_tune_settings(fe,
&fetunesettings) == 0)) {
fepriv->min_delay = (fetunesettings.min_delay_ms * HZ) / 1000;
fepriv->max_drift = fetunesettings.max_drift;
fepriv->step_size = fetunesettings.step_size;
} else {
/* default values */
...


> > > 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.
> > >
> >
> > As far as I know, Helene does not have automatic scan mechanism in
> > hardware.
>
> Ok, so the driver is doing the right thing here.
>
> > > If it does in hardware, you could add a get_frontend_algo() routine
> > > at helene driver and return DVBFE_ALGO_HW. The tuning zigzag software
> > > 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.
> > >
> >
> > 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.
>
> Yeah, but, after double-checking the logic, for ISDB-S, it will
> use:
>
> c->symbol_rate = 28860000;
> c->rolloff = ROLLOFF_35;
> c->bandwidth_hz = c->symbol_rate / 100 * 135;
>
> That would actually set the ISDB-S channel separation to 38.961 MHz.
>
> By setting symbol_rate like that, the zigzag for ISDB-S will
> be defined by:
>
> fepriv->step_size = c->symbol_rate / 16000; /* 38.961MHz / 16000 =
.002435
> - e. g. steps of ~25 kHz */
> fepriv->max_drift = c->symbol_rate / 2000; /* 38.961MHz / 2000 =
.0194805
> - e. g. max drift of ~195 kHz */
>
> Funny enough, it will be using about 25 kHz as step size for ISDB-S.
>
> 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.
>
> Thanks,
> Mauro

Hmm, interesting. I don't know zigzag for ISDB-S too, sorry...

Anyway, I don't worry about that. I said in above, we can use
get_tune_settings() for fine tuning.


Regards,
--
Katsuhiro Suzuki



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