media: dvb-frontends: a8293: fix LNB powerup failure in PCTV 461e

Fixes a8293 failure to raise LNB voltage in PCTV 461e DVB-S2 Stick
affecting multiple users over several years as found here:

http://www.linuxquestions.org/questions/linux-hardware-18/pctv-dvb-s2-stick-461e-not-feeding-lnb-4175529374/
https://www.linuxtv.org/wiki/index.php/Pinnacle_PCTV_DVB-S2_Stick_(461e)
https://github.com/OpenELEC/OpenELEC.tv/issues/3731

Caused by vIN undervoltage lockout (status register bit 7) when raising LNB to 18V.
Addressed by using the higher-precision voltages available on the a8293 to gradually
increase (slew) the voltage when voltage increases are requested.

Adds volt_slew_nanos_per_mv to a8293_platform_data struct for specifying slew rate.
If value is <1 or non-sane (>1600), the original no-slew version for a8293_set_voltage is used.

Link: https://lore.kernel.org/linux-media/20211231035326.6759-1-cjritola@gmail.com
[mchehab: fixed some coding style issues]
Signed-off-by: Chuck Ritola <cjritola@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/dvb-frontends/a8293.c

@@ -7,12 +7,139 @@
 
 #include "a8293.h"
 
+#define A8293_FLAG_ODT			0x10
+
 struct a8293_dev {
 	struct i2c_client *client;
 	u8 reg[2];
+	int volt_slew_nanos_per_mv;
 };
 
-static int a8293_set_voltage(struct dvb_frontend *fe,
+/*
+ * When increasing voltage, do so in minimal steps over time, minimizing
+ * risk of vIN undervoltage.
+ */
+
+static int a8293_set_voltage_slew(struct a8293_dev *dev,
+				  struct i2c_client *client,
+				  enum fe_sec_voltage fe_sec_voltage,
+				  int min_nanos_per_mv)
+{
+	int ret;
+	u8 reg0, reg1;
+	int new_volt_idx;
+	const int idx_to_mv[] = {
+		0,    12709, 13042, 13375, 14042, 15042, 18042, 18709, 19042
+	};
+	const u8 idx_to_reg[] = {
+		0x00, 0x20,  0x21,  0x22,  0x24,  0x27,  0x28,  0x2A,  0x2B
+	};
+	int this_volt_idx;
+	u8 status;
+	int prev_volt_idx;
+
+	dev_dbg(&client->dev, "set_voltage_slew fe_sec_voltage=%d\n",
+		fe_sec_voltage);
+
+	/* Read status register to clear any stale faults. */
+	ret = i2c_master_recv(client, &status, 1);
+	if (ret < 0)
+		goto err;
+
+	/* Determine previous voltage */
+	switch (dev->reg[0] & 0x2F) {
+	case 0x00:
+		prev_volt_idx = 0;
+		break;
+	case 0x20:
+		prev_volt_idx = 1;
+		break;
+	case 0x21:
+		prev_volt_idx = 2;
+		break;
+	case 0x22:
+		prev_volt_idx = 3;
+		break;
+	case 0x24:
+		prev_volt_idx = 4;
+		break;
+	case 0x27:
+		prev_volt_idx = 5;
+		break;
+	case 0x28:
+		prev_volt_idx = 6;
+		break;
+	case 0x2A:
+		prev_volt_idx = 7;
+		break;
+	case 0x2B:
+		prev_volt_idx = 8;
+		break;
+	default:
+		prev_volt_idx = 0;
+	}
+
+	/* Determine new voltage */
+	switch (fe_sec_voltage) {
+	case SEC_VOLTAGE_OFF:
+		new_volt_idx = 0;
+		break;
+	case SEC_VOLTAGE_13:
+		new_volt_idx = 2;
+		break;
+	case SEC_VOLTAGE_18:
+		new_volt_idx = 6;
+		break;
+	default:
+		ret = -EINVAL;
+		goto err;
+	}
+
+	/* Slew to new voltage if new voltage is greater than current voltage */
+	this_volt_idx = prev_volt_idx;
+	if (this_volt_idx < new_volt_idx) {
+		while (this_volt_idx < new_volt_idx) {
+			int delta_mv = idx_to_mv[this_volt_idx+1] - idx_to_mv[this_volt_idx];
+			int min_wait_time = delta_mv * min_nanos_per_mv;
+
+			reg0 = idx_to_reg[this_volt_idx+1];
+			reg0 |= A8293_FLAG_ODT;
+
+			ret = i2c_master_send(client, &reg0, 1);
+			if (ret < 0)
+				goto err;
+			dev->reg[0] = reg0;
+			this_volt_idx++;
+			usleep_range(min_wait_time, min_wait_time * 2);
+		}
+	} else { /* Else just set the voltage */
+		reg0 = idx_to_reg[new_volt_idx];
+		reg0 |= A8293_FLAG_ODT;
+		ret = i2c_master_send(client, &reg0, 1);
+		if (ret < 0)
+			goto err;
+		dev->reg[0] = reg0;
+	}
+
+	/* TMODE=0, TGATE=1 */
+	reg1 = 0x82;
+	if (reg1 != dev->reg[1]) {
+		ret = i2c_master_send(client, &reg1, 1);
+		if (ret < 0)
+			goto err;
+		dev->reg[1] = reg1;
+	}
+
+	usleep_range(1500, 5000);
+
+	return 0;
+err:
+	dev_dbg(&client->dev, "failed=%d\n", ret);
+	return ret;
+}
+
+
+static int a8293_set_voltage_noslew(struct dvb_frontend *fe,
 				    enum fe_sec_voltage fe_sec_voltage)
 {
 	struct a8293_dev *dev = fe->sec_priv;
@@ -20,7 +147,8 @@ static int a8293_set_voltage(struct dvb_frontend *fe,
 	int ret;
 	u8 reg0, reg1;
 
-	dev_dbg(&client->dev, "fe_sec_voltage=%d\n", fe_sec_voltage);
+	dev_dbg(&client->dev, "set_voltage_noslew fe_sec_voltage=%d\n",
+		fe_sec_voltage);
 
 	switch (fe_sec_voltage) {
 	case SEC_VOLTAGE_OFF:
@@ -62,6 +190,26 @@ static int a8293_set_voltage(struct dvb_frontend *fe,
 	return ret;
 }
 
+static int a8293_set_voltage(struct dvb_frontend *fe,
+			     enum fe_sec_voltage fe_sec_voltage)
+{
+	struct a8293_dev *dev = fe->sec_priv;
+	struct i2c_client *client = dev->client;
+	int volt_slew_nanos_per_mv = dev->volt_slew_nanos_per_mv;
+
+	dev_dbg(&client->dev, "set_voltage volt_slew_nanos_per_mv=%d\n",
+		volt_slew_nanos_per_mv);
+
+	/* Use slew version if slew rate is set to a sane value */
+	if (volt_slew_nanos_per_mv > 0 && volt_slew_nanos_per_mv < 1600)
+		a8293_set_voltage_slew(dev, client, fe_sec_voltage,
+				       volt_slew_nanos_per_mv);
+	else
+		a8293_set_voltage_noslew(fe, fe_sec_voltage);
+
+	return 0;
+}
+
 static int a8293_probe(struct i2c_client *client)
 {
 	struct a8293_dev *dev;
@@ -77,6 +225,7 @@ static int a8293_probe(struct i2c_client *client)
 	}
 
 	dev->client = client;
+	dev->volt_slew_nanos_per_mv = pdata->volt_slew_nanos_per_mv;
 
 	/* check if the SEC is there */
 	ret = i2c_master_recv(client, buf, 2);

drivers/media/dvb-frontends/a8293.h

@@ -18,9 +18,12 @@
 /**
  * struct a8293_platform_data - Platform data for the a8293 driver
  * @dvb_frontend: DVB frontend.
+ * @volt_slew_nanos_per_mv: Slew rate when increasing LNB voltage,
+ *	 in nanoseconds per millivolt.
  */
 struct a8293_platform_data {
 	struct dvb_frontend *dvb_frontend;
+	int volt_slew_nanos_per_mv;
 };
 
 #endif /* A8293_H */

drivers/media/usb/em28xx/em28xx-dvb.c

@@ -1204,6 +1204,12 @@ static int em28178_dvb_init_pctv_461e(struct em28xx *dev)
 
 	/* attach SEC */
 	a8293_pdata.dvb_frontend = dvb->fe[0];
+	/*
+	 * 461e has a tendency to have vIN undervoltage troubles.
+	 * Slew mitigates this.
+	 */
+	a8293_pdata.volt_slew_nanos_per_mv = 20;
+
 	dvb->i2c_client_sec = dvb_module_probe("a8293", NULL,
 					       &dev->i2c_adap[dev->def_i2c_bus],
 					       0x08, &a8293_pdata);