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Date:   Sat, 2 May 2020 07:58:33 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
To:     "Daniel W. S. Almeida" <dwlsalmeida@gmail.com>
Cc:     sean@mess.org, kstewart@linuxfoundation.org, allison@lohutok.net,
        tglx@linutronix.de, linux-media@vger.kernel.org,
        skhan@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC, WIP, v4 03/11] media: vidtv: implement a demodulator
 driver
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In-Reply-To: <20200502032216.197977-4-dwlsalmeida@gmail.com>
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        <20200502032216.197977-4-dwlsalmeida@gmail.com>
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Em Sat,  2 May 2020 00:22:08 -0300
"Daniel W. S. Almeida" <dwlsalmeida@gmail.com> escreveu:

> From: "Daniel W. S. Almeida" <dwlsalmeida@gmail.com>
> 
> Implement a I2C demodulator driver, simulating support for DVB-T, DVB-C
> and DVB-S.
> 
> This demodulator will periodically check the signal quality against a table
> and drop the TS lock if it drops below a threshold value, regaining it in
> the event that the signal improves.
> 
> Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
> ---
>  drivers/media/test-drivers/vidtv/Makefile     |   2 +-
>  .../media/test-drivers/vidtv/vidtv_demod.c    | 493 ++++++++++++++++++
>  .../media/test-drivers/vidtv/vidtv_demod.h    |  43 ++
>  3 files changed, 537 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/media/test-drivers/vidtv/vidtv_demod.c
>  create mode 100644 drivers/media/test-drivers/vidtv/vidtv_demod.h
> 
> diff --git a/drivers/media/test-drivers/vidtv/Makefile b/drivers/media/test-drivers/vidtv/Makefile
> index e625810a82603..36ba00ddc0d1e 100644
> --- a/drivers/media/test-drivers/vidtv/Makefile
> +++ b/drivers/media/test-drivers/vidtv/Makefile
> @@ -1,3 +1,3 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
> -obj-$(CONFIG_DVB_VIDTV)	+= vidtv_tuner.o
> +obj-$(CONFIG_DVB_VIDTV)	+= vidtv_tuner.o  vidtv_demod.o
> diff --git a/drivers/media/test-drivers/vidtv/vidtv_demod.c b/drivers/media/test-drivers/vidtv/vidtv_demod.c
> new file mode 100644
> index 0000000000000..e5f157e4bbe48
> --- /dev/null
> +++ b/drivers/media/test-drivers/vidtv/vidtv_demod.c
> @@ -0,0 +1,493 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * The Virtual DVB test driver serves as a reference DVB driver and helps
> + * validate the existing APIs in the media subsystem. It can also aid
> + * developers working on userspace applications.
> + *
> + * Written by Daniel W. S. Almeida <dwlsalmeida@gmail.com>
> + * Based on the example driver written by Emard <emard@softhome.net>
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/string.h>
> +#include <linux/slab.h>
> +#include <linux/workqueue.h>
> +#include <linux/random.h>
> +#include <linux/errno.h>
> +#include <linux/i2c.h>
> +#include <media/dvb_frontend.h>
> +#include "vidtv_demod.h"
> +
> +MODULE_DESCRIPTION("Virtual DVB Demodulator Driver");
> +MODULE_AUTHOR("Daniel W. S. Almeida");
> +MODULE_LICENSE("GPL");
> +
> +struct vidtv_demod_cnr_to_qual_s vidtv_demod_c_cnr_2_qual[] = {
> +	/* from libdvbv5 source code, in milli db */
> +	{ QAM_256, FEC_NONE,  34000, 38000},
> +	{ QAM_64,  FEC_NONE,  30000, 34000},
> +};
> +
> +struct vidtv_demod_cnr_to_qual_s vidtv_demod_s_cnr_2_qual[] = {
> +	/* from libdvbv5 source code, in milli db */
> +	{ QPSK, FEC_1_2,  7000, 10000},
> +	{ QPSK, FEC_2_3,  9000, 12000},
> +	{ QPSK, FEC_3_4, 10000, 13000},
> +	{ QPSK, FEC_5_6, 11000, 14000},
> +	{ QPSK, FEC_7_8, 12000, 15000},
> +};
> +
> +struct vidtv_demod_cnr_to_qual_s vidtv_demod_s2_cnr_2_qual[] = {
> +	/* from libdvbv5 source code, in milli db */
> +	{ QPSK,  FEC_1_2,   9000,  12000},
> +	{ QPSK,  FEC_2_3,  11000,  14000},
> +	{ QPSK,  FEC_3_4,  12000,  15000},
> +	{ QPSK,  FEC_5_6,  12000,  15000},
> +	{ QPSK,  FEC_8_9,  13000,  16000},
> +	{ QPSK,  FEC_9_10, 13500,  16500},
> +	{ PSK_8, FEC_2_3,  14500,  17500},
> +	{ PSK_8, FEC_3_4,  16000,  19000},
> +	{ PSK_8, FEC_5_6,  17500,  20500},
> +	{ PSK_8, FEC_8_9,  19000,  22000},
> +};
> +
> +static struct vidtv_demod_cnr_to_qual_s vidtv_demod_t_cnr_2_qual[] = {
> +	/* from libdvbv5 source code, in milli db*/
> +	{   QPSK, FEC_1_2,  4100,  5900},
> +	{   QPSK, FEC_2_3,  6100,  9600},
> +	{   QPSK, FEC_3_4,  7200, 12400},
> +	{   QPSK, FEC_5_6,  8500, 15600},
> +	{   QPSK, FEC_7_8,  9200, 17500},
> +
> +	{ QAM_16, FEC_1_2,  9800, 11800},
> +	{ QAM_16, FEC_2_3, 12100, 15300},
> +	{ QAM_16, FEC_3_4, 13400, 18100},
> +	{ QAM_16, FEC_5_6, 14800, 21300},
> +	{ QAM_16, FEC_7_8, 15700, 23600},
> +
> +	{ QAM_64, FEC_1_2, 14000, 16000},
> +	{ QAM_64, FEC_2_3, 19900, 25400},
> +	{ QAM_64, FEC_3_4, 24900, 27900},
> +	{ QAM_64, FEC_5_6, 21300, 23300},
> +	{ QAM_64, FEC_7_8, 22000, 24000},
> +};
> +
> +static struct vidtv_demod_cnr_to_qual_s
> +*vidtv_match_cnr_s(struct dvb_frontend *fe)
> +{
> +	struct dtv_frontend_properties *c;
> +	struct vidtv_demod_cnr_to_qual_s *cnr2qual = NULL;
> +	u32    array_size                          = 0;
> +	u32 i;
> +
> +	c = &fe->dtv_property_cache;
> +
> +	switch (c->delivery_system) {
> +	case SYS_DVBT:
> +	case SYS_DVBT2:
> +		cnr2qual   = vidtv_demod_t_cnr_2_qual;
> +		array_size = ARRAY_SIZE(vidtv_demod_t_cnr_2_qual);
> +		break;
> +
> +	case SYS_DVBS:
> +		cnr2qual   = vidtv_demod_s_cnr_2_qual;
> +		array_size = ARRAY_SIZE(vidtv_demod_s_cnr_2_qual);
> +		break;
> +
> +	case SYS_DVBS2:
> +		cnr2qual   = vidtv_demod_s2_cnr_2_qual;
> +		array_size = ARRAY_SIZE(vidtv_demod_s2_cnr_2_qual);
> +		break;
> +
> +	case SYS_DVBC_ANNEX_A:
> +		cnr2qual   = vidtv_demod_c_cnr_2_qual;
> +		array_size = ARRAY_SIZE(vidtv_demod_c_cnr_2_qual);
> +		break;
> +
> +	default:
> +		pr_warn("%s: unsupported delivery system: %u\n",
> +			__func__,
> +			c->delivery_system);
> +		break;
> +	}
> +
> +	for (i = 0; i <= array_size; i++)
> +		if (cnr2qual[i].modulation == c->modulation &&
> +		    cnr2qual[i].fec == c->fec_inner)
> +			return &cnr2qual[i];
> +
> +	return NULL; /* not found */
> +}
> +
> +static void vidtv_demod_poll_snr_handler(struct work_struct *work)
> +{
> +	/*
> +	 * periodically check the signal quality and eventually
> +	 * lose the TS lock if it dips too low
> +	 */
> +	struct vidtv_demod_state *state;
> +	struct dtv_frontend_properties *c;
> +	struct vidtv_demod_cnr_to_qual_s *cnr2qual = NULL;
> +	struct vidtv_demod_config *config;
> +	u16 snr = 0;
> +
> +	state  = container_of(work, struct vidtv_demod_state, poll_snr.work);
> +	c      = &state->frontend.dtv_property_cache;
> +	config = &state->config;
> +
> +	if (!state->frontend.ops.tuner_ops.get_rf_strength)
> +		return;
> +
> +	state->frontend.ops.tuner_ops.get_rf_strength(&state->frontend, &snr);
> +
> +	cnr2qual = vidtv_match_cnr_s(&state->frontend);
> +	if (!cnr2qual)
> +		return;
> +
> +	if (snr < cnr2qual->cnr_ok) {
> +		/* eventually lose the TS lock */
> +		if (prandom_u32_max(100) < config->drop_tslock_prob_on_low_snr)
> +			state->status = 0;
> +	} else {
> +		/* recover if the signal improves */
> +		if (prandom_u32_max(100) <
> +		    config->recover_tslock_prob_on_good_snr)
> +			state->status = FE_HAS_SIGNAL  |
> +					FE_HAS_CARRIER |
> +					FE_HAS_VITERBI |
> +					FE_HAS_SYNC    |
> +					FE_HAS_LOCK;
> +	}
> +
> +	schedule_delayed_work(&state->poll_snr, msecs_to_jiffies(2000));

I would place the time (2000) on a #define at the top.

> +}
> +
> +static int vidtv_demod_read_status(struct dvb_frontend *fe,
> +				   enum fe_status *status)
> +{
> +	struct vidtv_demod_state *state = fe->demodulator_priv;
> +
> +	*status = state->status;
> +
> +	return 0;
> +}

> +static int vidtv_demod_read_ber(struct dvb_frontend *fe, u32 *ber)
> +{
> +	*ber = 0;
> +	return 0;
> +}
> +
> +static int vidtv_demod_read_signal_strength(struct dvb_frontend *fe,
> +					    u16 *strength)
> +{
> +	*strength = 0;
> +	return 0;
> +}
> +
> +static int vidtv_demod_read_snr(struct dvb_frontend *fe, u16 *snr)
> +{
> +	*snr = 0;
> +	return 0;
> +}
> +
> +static int vidtv_demod_read_ucblocks(struct dvb_frontend *fe, u32 *ucblocks)
> +{
> +	*ucblocks = 0;
> +	return 0;
> +}

Hmm... I'm actually in doubt about the above legacy DVB-3 ops.

Let's keep it for now, but I may submit a patch to dvb-core for it
to use the data from the cache, if someone use those legacy ioctls
and the corresponding fe->ops is not defined by a demod.

> +
> +/*
> + * Should only be implemented if it actually reads something from the hardware.
> + * Also, it should check for the locks, in order to avoid report wrong data
> + * to userspace.
> + */

I would rewrite it as:

/*
 * NOTE:
 * This is implemented here just to be used as an example for real
 * demod drivers.
 *
 * Should only be implemented if it actually reads something from the hardware.
 * Also, it should check for the locks, in order to avoid report wrong data
 * to userspace.
 */


> +static int vidtv_demod_get_frontend(struct dvb_frontend *fe,
> +				    struct dtv_frontend_properties *p)
> +{
> +	return 0;
> +}
> +
> +static int vidtv_demod_set_frontend(struct dvb_frontend *fe)
> +{
> +	struct vidtv_demod_state *state            = fe->demodulator_priv;
> +	struct vidtv_demod_cnr_to_qual_s *cnr2qual = NULL;
> +	u32    tuner_status                        = 0;
> +
> +	if (fe->ops.tuner_ops.set_params) {
> +		fe->ops.tuner_ops.set_params(fe);
> +
> +		/* store the CNR returned by the tuner */
> +		fe->ops.tuner_ops.get_rf_strength(fe, &state->tuner_cnr);
> +
> +		fe->ops.tuner_ops.get_status(fe, &tuner_status);
> +		state->status = (state->tuner_cnr > 0) ?  FE_HAS_SIGNAL  |
> +							  FE_HAS_CARRIER |
> +							  FE_HAS_VITERBI |
> +							  FE_HAS_SYNC    |
> +							  FE_HAS_LOCK	 :
> +							  0;
> +		cnr2qual = vidtv_match_cnr_s(fe);
> +
> +		/* signal isn't good: might lose the lock eventually */
> +		if (tuner_status == TUNER_STATUS_LOCKED &&
> +		    state->tuner_cnr < cnr2qual->cnr_good) {
> +			schedule_delayed_work(&state->poll_snr,
> +					      msecs_to_jiffies(2000));

Use the same define as above mentioned for the msecs time.

> +
> +			state->poll_snr_thread_running = true;
> +		}
> +
> +		if (fe->ops.i2c_gate_ctrl)
> +			fe->ops.i2c_gate_ctrl(fe, 0);
> +	}
> +
> +	return 0;
> +}
> +
> +static int vidtv_demod_sleep(struct dvb_frontend *fe)
> +{
> +	struct vidtv_demod_state *state = fe->demodulator_priv;
> +
> +	if (state->poll_snr_thread_running) {
> +		cancel_delayed_work_sync(&state->poll_snr);
> +		state->poll_snr_thread_running = false;
> +		state->poll_snr_thread_restart = true;
> +	}
> +	return 0;
> +}
> +
> +static int vidtv_demod_init(struct dvb_frontend *fe)
> +{
> +	struct vidtv_demod_state *state = fe->demodulator_priv;
> +	u32    tuner_status             = 0;
> +
> +	if (state->cold_start)
> +		INIT_DELAYED_WORK(&state->poll_snr,
> +				  &vidtv_demod_poll_snr_handler);
> +
> +	/*
> +	 * At resume, start the snr poll thread only if it was suspended with
> +	 * the thread running. Extra care should be taken here, as some tuner
> +	 * status change might happen at resume time (for example, due to a
> +	 * ioctl syscall to set_frontend, or due to a release syscall).

typo: "a ioctl" -> "an ioctl"

> +	 */
> +	fe->ops.tuner_ops.get_status(fe, &tuner_status);
> +
> +	if (tuner_status == TUNER_STATUS_LOCKED &&
> +	    state->poll_snr_thread_restart) {
> +		schedule_delayed_work(&state->poll_snr,
> +				      msecs_to_jiffies(2000));

Same note about the timing constant. Keep all those "2000" inside
something like:

	$define POLL_THREAD_TIME	2000	/* msecs */

> +
> +		state->poll_snr_thread_restart = false;
> +	}
> +
> +	state->cold_start = false;
> +	return 0;
> +}
> +


> +static int vidtv_demod_set_tone(struct dvb_frontend *fe,
> +				enum fe_sec_tone_mode tone)
> +{
> +	return 0;
> +}
> +
> +static int vidtv_demod_set_voltage(struct dvb_frontend *fe,
> +				   enum fe_sec_voltage voltage)
> +{
> +	return 0;
> +}


It would be worth adding a note for each of the above stating
that they should be implemented only if if the demod has support
for DVB/S and/or DVB/S2

> +static void vidtv_demod_release(struct dvb_frontend *fe)
> +{
> +	struct vidtv_demod_state *state = fe->demodulator_priv;
> +
> +	if (state->poll_snr_thread_running)
> +		cancel_delayed_work_sync(&state->poll_snr);
> +
> +	kfree(state);
> +}
> +
> +static const struct dvb_frontend_ops vidtv_demod_ofdm_ops = {
> +	.delsys = { SYS_DVBT },
> +	.info   = {
> +		.name                  = "Dummy DVB-T",
> +		.frequency_min_hz      = 0,
> +		.frequency_max_hz      = 863250 * kHz,
> +		.frequency_stepsize_hz = 62500,
> +		.caps                  = FE_CAN_FEC_1_2 |
> +					 FE_CAN_FEC_2_3 |
> +					 FE_CAN_FEC_3_4 |
> +					 FE_CAN_FEC_4_5 |
> +					 FE_CAN_FEC_5_6 |
> +					 FE_CAN_FEC_6_7 |
> +					 FE_CAN_FEC_7_8 |
> +					 FE_CAN_FEC_8_9 |
> +					 FE_CAN_FEC_AUTO |
> +					 FE_CAN_QAM_16 |
> +					 FE_CAN_QAM_64 |
> +					 FE_CAN_QAM_AUTO |
> +					 FE_CAN_TRANSMISSION_MODE_AUTO |
> +					 FE_CAN_GUARD_INTERVAL_AUTO |
> +					 FE_CAN_HIERARCHY_AUTO,
> +	},
> +
> +	.release = vidtv_demod_release,
> +
> +	.init  = vidtv_demod_init,
> +	.sleep = vidtv_demod_sleep,
> +
> +	.set_frontend = vidtv_demod_set_frontend,
> +	.get_frontend = vidtv_demod_get_frontend,
> +
> +	.read_status          = vidtv_demod_read_status,
> +	.read_ber             = vidtv_demod_read_ber,
> +	.read_signal_strength = vidtv_demod_read_signal_strength,
> +	.read_snr             = vidtv_demod_read_snr,
> +	.read_ucblocks        = vidtv_demod_read_ucblocks,
> +};
> +
> +static const struct dvb_frontend_ops vidtv_demod_qam_ops = {
> +	.delsys = { SYS_DVBC_ANNEX_A },
> +	.info   = {
> +		.name                  = "Dummy DVB-C",
> +		.frequency_min_hz      = 51 * MHz,
> +		.frequency_max_hz      = 858 * MHz,
> +		.frequency_stepsize_hz = 62500,
> +		/* symbol_rate_min: SACLK/64 == (XIN/2)/64 */
> +		.symbol_rate_min = (57840000 / 2) / 64,
> +		.symbol_rate_max = (57840000 / 2) / 4,    /* SACLK/4 */
> +		.caps            = FE_CAN_QAM_16 |
> +				   FE_CAN_QAM_32 |
> +				   FE_CAN_QAM_64 |
> +				   FE_CAN_QAM_128 |
> +				   FE_CAN_QAM_256 |
> +				   FE_CAN_FEC_AUTO |
> +				   FE_CAN_INVERSION_AUTO
> +	},
> +
> +	.release = vidtv_demod_release,
> +
> +	.init  = vidtv_demod_init,
> +	.sleep = vidtv_demod_sleep,
> +
> +	.set_frontend = vidtv_demod_set_frontend,
> +	.get_frontend = vidtv_demod_get_frontend,
> +
> +	.read_status          = vidtv_demod_read_status,
> +	.read_ber             = vidtv_demod_read_ber,
> +	.read_signal_strength = vidtv_demod_read_signal_strength,
> +	.read_snr             = vidtv_demod_read_snr,
> +	.read_ucblocks        = vidtv_demod_read_ucblocks,
> +};
> +
> +static const struct dvb_frontend_ops vidtv_demod_qpsk_ops = {
> +	.delsys = { SYS_DVBS },
> +	.info   = {
> +		.name                   = "Dummy DVB-S",
> +		.frequency_min_hz       = 950 * MHz,
> +		.frequency_max_hz       = 2150 * MHz,
> +		.frequency_stepsize_hz  = 250 * kHz,
> +		.frequency_tolerance_hz = 29500 * kHz,
> +		.symbol_rate_min        = 1000000,
> +		.symbol_rate_max        = 45000000,
> +		.caps                   = FE_CAN_INVERSION_AUTO |
> +					  FE_CAN_FEC_1_2 |
> +					  FE_CAN_FEC_2_3 |
> +					  FE_CAN_FEC_3_4 |
> +					  FE_CAN_FEC_5_6 |
> +					  FE_CAN_FEC_7_8 |
> +					  FE_CAN_FEC_AUTO |
> +					  FE_CAN_QPSK
> +	},
> +
> +	.release = vidtv_demod_release,
> +
> +	.init  = vidtv_demod_init,
> +	.sleep = vidtv_demod_sleep,
> +
> +	.set_frontend = vidtv_demod_set_frontend,
> +	.get_frontend = vidtv_demod_get_frontend,
> +
> +	.read_status          = vidtv_demod_read_status,
> +	.read_ber             = vidtv_demod_read_ber,
> +	.read_signal_strength = vidtv_demod_read_signal_strength,
> +	.read_snr             = vidtv_demod_read_snr,
> +	.read_ucblocks        = vidtv_demod_read_ucblocks,
> +
> +	.set_voltage = vidtv_demod_set_voltage,
> +	.set_tone    = vidtv_demod_set_tone,
> +};

The recommended way is to place everything on a single entry:

    static const struct dvb_frontend_ops vidtv_demod_ops = {
	.delsys = {
		SYS_DVBT,
		SYS_DVBT2,
		SYS_DVBC_ANNEX_A,
		SYS_DVBS,
		SYS_DVBS2,
	},
	.info   = {
		.name                  = "Dummy demod for DVB-T/T2/C/S/S2",
		.frequency_min_hz      = 51 * MHz,
		.frequency_max_hz       = 2150 * MHz,
		.frequency_stepsize_hz = 62500,
		.frequency_tolerance_hz = 29500 * kHz,
		.symbol_rate_min        = 1000000,
		.symbol_rate_max        = 45000000,
		
		.caps                  =    FE_CAN_FEC_1_2 |
					    FE_CAN_FEC_2_3 |
					    FE_CAN_FEC_3_4 |
					    FE_CAN_FEC_4_5 |
					    FE_CAN_FEC_5_6 |
					    FE_CAN_FEC_6_7 |
					    FE_CAN_FEC_7_8 |
					    FE_CAN_FEC_8_9 |
					    FE_CAN_FEC_AUTO |
					    FE_CAN_QAM_16 |
					    FE_CAN_QAM_64 |
					    FE_CAN_QAM_32 |
					    FE_CAN_QAM_128 |
					    FE_CAN_QAM_256 |
					    FE_CAN_QAM_AUTO |
					    FE_CAN_QPSK |
					    FE_CAN_FEC_AUTO |
					    FE_CAN_INVERSION_AUTO |
					    FE_CAN_TRANSMISSION_MODE_AUTO |
					    FE_CAN_GUARD_INTERVAL_AUTO |
					    FE_CAN_HIERARCHY_AUTO,
	},

	.release = vidtv_demod_release,

	.init  = vidtv_demod_init,
	.sleep = vidtv_demod_sleep,

	.set_frontend = vidtv_demod_set_frontend,
	.get_frontend = vidtv_demod_get_frontend,

	.read_status          = vidtv_demod_read_status,
	.read_ber             = vidtv_demod_read_ber,
	.read_signal_strength = vidtv_demod_read_signal_strength,
	.read_snr             = vidtv_demod_read_snr,
	.read_ucblocks        = vidtv_demod_read_ucblocks,
	

	/* For DVB-S/S2 */
	.set_voltage = vidtv_demod_set_voltage,
	.set_tone    = vidtv_demod_set_tone,	
    };

> +
> +static const struct i2c_device_id vidtv_demod_i2c_id_table[] = {
> +	{"vidtv_demod", 0},
> +	{}
> +};
> +MODULE_DEVICE_TABLE(i2c, vidtv_demod_i2c_id_table);
> +
> +static int vidtv_demod_i2c_probe(struct i2c_client *client,
> +				 const struct i2c_device_id *id)
> +{
> +	struct vidtv_demod_config *config = client->dev.platform_data;
> +	struct vidtv_demod_state *state;
> +	const struct dvb_frontend_ops *ops;
> +
> +	/* allocate memory for the internal state */
> +	state = kzalloc(sizeof(*state), GFP_KERNEL);
> +	if (!state)
> +		return -ENOMEM;
> +
> +	switch (config->chosen_delsys) {
> +	case SYS_DVBT:
> +		ops = &vidtv_demod_ofdm_ops;
> +		break;
> +	case SYS_DVBC_ANNEX_A:
> +		ops = &vidtv_demod_qam_ops;
> +		break;
> +	case SYS_DVBS:
> +		ops = &vidtv_demod_qpsk_ops;
> +		break;
> +	default:
> +		pr_err("%s: Unsupported delivery system. Falling back to DVB-T",
> +		       __func__);
> +		ops = &vidtv_demod_ofdm_ops;
> +		break;
> +	}

By placing everything into a single entry, you can get rid of the above.

Nowadays, most demods are multi-standard. So, let's teach people to write
just a single entry for it, instead of the legacy way of one entry per
each delivery system.

> +
> +	/* create dvb_frontend */
> +	memcpy(&state->frontend.ops,
> +	       ops,
> +	       sizeof(struct dvb_frontend_ops));
> +
> +	state->frontend.demodulator_priv = state;
> +	/* return the pointer to the bridge driver */
> +	config->frontend = &state->frontend;
> +	i2c_set_clientdata(client, state);
> +
> +	return 0;
> +}
> +
> +static int vidtv_demod_i2c_remove(struct i2c_client *client)
> +{
> +	struct vidtv_demod_state *state = i2c_get_clientdata(client);
> +
> +	memset(&state->frontend.ops, 0, sizeof(struct dvb_frontend_ops));
> +	state->frontend.demodulator_priv = NULL;
> +	kfree(state);
> +
> +	return 0;
> +}
> +
> +static struct i2c_driver vidtv_demod_i2c_driver = {
> +	.driver = {
> +		.name                = "vidtv_demod",
> +		.suppress_bind_attrs = true,
> +	},
> +	.probe    = vidtv_demod_i2c_probe,
> +	.remove   = vidtv_demod_i2c_remove,
> +	.id_table = vidtv_demod_i2c_id_table,
> +};
> +
> +module_i2c_driver(vidtv_demod_i2c_driver);
> diff --git a/drivers/media/test-drivers/vidtv/vidtv_demod.h b/drivers/media/test-drivers/vidtv/vidtv_demod.h
> new file mode 100644
> index 0000000000000..49c2a43f71661
> --- /dev/null
> +++ b/drivers/media/test-drivers/vidtv/vidtv_demod.h
> @@ -0,0 +1,43 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * The Virtual DTV test driver serves as a reference DVB driver and helps
> + * validate the existing APIs in the media subsystem. It can also aid
> + * developers working on userspace applications.
> + *
> + * Written by Daniel W. S. Almeida <dwlsalmeida@gmail.com>
> + * Based on the example driver written by Emard <emard@softhome.net>
> + */
> +
> +#ifndef VIDTV_DEMOD_H
> +#define VIDTV_DEMOD_H
> +
> +#include <linux/dvb/frontend.h>
> +#include <media/dvb_frontend.h>
> +
> +struct vidtv_demod_cnr_to_qual_s {
> +	/* attempt to use the same values as libdvbv5 */
> +	u32 modulation;
> +	u32 fec;
> +	u32 cnr_ok, cnr_good;
> +};
> +
> +struct vidtv_demod_config {
> +	struct dvb_frontend *frontend;
> +	/* probability of losing the lock due to low snr */
> +	u8 drop_tslock_prob_on_low_snr;
> +	/* probability of recovering when the signal improves */
> +	u8 recover_tslock_prob_on_good_snr;
> +	u8 chosen_delsys;
> +};
> +
> +struct vidtv_demod_state {
> +	struct dvb_frontend frontend;
> +	struct vidtv_demod_config config;
> +	struct delayed_work poll_snr;
> +	enum fe_status status;
> +	u16 tuner_cnr;
> +	bool cold_start;
> +	bool poll_snr_thread_running;
> +	bool poll_snr_thread_restart;
> +};
> +#endif // VIDTV_DEMOD_H


Thanks,
Mauro