Samsung Galaxy Tab A 8.0 2015 (samsung-gt58)

From postmarketOS Wiki
Note This page is about the dedicated port of this device. There is also an optional generic port available for this device - see Generic MSM8916 (qcom-msm8916).
Samsung Galaxy Tab A 8.0 (2015)
Samsung Galaxy Tab A 8.0 LTE (SM-T355Y)
Samsung Galaxy Tab A 8.0 LTE (SM-T355Y)
Manufacturer Samsung
Name Galaxy Tab A 8.0 (2015)
Codename samsung-gt58
Released 2015
Type tablet
Hardware
Chipset Qualcomm Snapdragon 410 (MSM8916)
CPU Quad-core 1.2 GHz Cortex-A53
GPU Qualcomm Adreno 306
Display 768x1024 (XGA) PLS
Storage 16 GB
Memory 2 GB
Architecture aarch64
Software
Original software Android
Original version 7.1.1 (Linux 3.10.49)
postmarketOS
Category community
Pre-built images yes
postmarketOS kernel Mainline
Unixbench Whet/Dhry score 921
Optional Generic Port Generic MSM8916 (qcom-msm8916)
Features
Flashing
Works
USB Networking
Works
Internal storage
SD card
Battery
Partial
Screen
Works
Touchscreen
Works
Multimedia
3D Acceleration
Works
Audio
Works
Camera
Camera Flash
Connectivity
WiFi
Works
Bluetooth
Works
GPS
Works
Modem
Calls
Works
SMS
Works
Mobile data
Works
Miscellaneous
FDE
Works
USB OTG
Broken
HDMI/DP
Sensors
Accelerometer
Works
Magnetometer
Ambient Light
Proximity
Hall Effect
Works
Haptics
This device is based on the Snapdragon 410.
See the SoC page for common tips, guides and troubleshooting steps

Samsung Galaxy Tab A (2015) is a series of devices based on Qualcomm Snapdragon 410 SoC which has great mainline Linux support.

This page should generally apply to any 8.0 inch variant of the device (WiFi, LTE, with and without the pen support). Note that those variants may have different amount of RAM. For 9.7 inch variants see Samsung Galaxy Tab A 9.7.

Variant differences

The device has multiple variants, the main differences in the features are shown in the table below:

Feature WIFI LTE Notes
GPS Partial Works WiFi: cli investigation WIP.
Mobile data Unavailable Works
SMS Unavailable Works
Calls Unavailable Works

Note: The WiFi variant gt58wifi chipset is APQ8016.

Contributors

  • Hello-world-321

Maintainer(s)

  • TravMurav

Users owning this device


How to enter flash mode

Download mode: When turned off hold Power + Volume Up + Home

lk2nd Fastboot: When turned off hold Power + Volume Down

Installation

lk2nd is a secondary bootloader that provides a standard fastboot interface, which can be used to boot postmarketOS without Android boot flashed or pmbootstrap flasher flash_kernel.

  1. Download lk2nd-msm8916.img from Releases page on Github.
  2. Boot your phone to bootloader (Odin/Download) mode by holding Volume Down and Home while powering up.
  3. Follow lk2nd instructions to install lk2nd. Basically flash it to the boot partition (heimdall flash --BOOT lk2nd-msm8916.img)
  4. Follow Qualcomm_Snapdragon_410/412_(MSM8916)#Installation to install postmarketOS.
Note Note: Enter lk2nd fastboot mode by pressing only Volume Down + Power (without Home). Pressing Home additionally will bring you to the Samsung Download mode.

Audio

Icon WARNING: The speakers are rather loud on 100% volume and may produce distorted sound that may damage your speakers after long use. Please make sure to use reasonable volumes - your ears and your speaker will thank you!

Known Bugs and Workarounds

  • Multi-touch doesn't work

This is a known issue: The touch controller sends the events in a different format that the driver can decode. Fix is WIP.

  • How to charge device ?

Charger driver is not present at this time. Turn off your device and plug it in. The device will boot and get charged. You can check if the device charges by reading the value from /sys/class/power_supply/max170xx_battery/current_now

Battery percentage /sys/class/power_supply/max170xx_battery/capacity

  • Display Artifacts during brightness adjustment

Turn display off (lock device using power button) and turn on again to remove artifacts until next brightness change. Auto brightness should be turned off due display bug.

  • Automatically switch to headset and turn off speakers when headset plugged in or cannot switch to speakers during phone calls

Select headset from settings after plugging in headset (Known issue)

Mainline Kernel Status

Table of components in the device

Component Model Mainline kernel driver Status
MicroUSB - Yes Working in kernel fork
eMMC (Android lists) Toshiba 400073 (Same as gt510wifi) Yes Working in kernel fork
Battery/Charging/Fuelgauge (Same as gt510wifi) MAX77849 ? Fuel gauge works using MAX77849 drivers
Volume/Power/Home keys GPIO Yes Working in kernel fork
Capacitive keys Part of Zinitix BT532 Touchscreen No Needs driver changes
Accelerometer STMicroelectronics (Same as gt510wifi and matissevewifi) Yes, supported in kernel fork Yes
Light Sensor Capella Micro CM3323 (Same as gt510wifi) Yes Yes
Display Samsung S6D7AA0 LSL080AL03 Yes Working in kernel fork
Backlight IC Texas Instruments lp8556 Not strictly needed Brightness is set through DSI, PWM signal goes to lp8556
Audio PM8916/NXP TFA9895 (Same as a3ulte) Yes Audio & Microphones Work. Speakers are powered by external amp (NXP TFA9895 or similar). Secondary Mic (On Device) uses gpio pin.
Touch Screen Zinitix BT532 Yes Working in kernel fork using BT541 Drivers. Drivers need modification to enable touchkeys.
USB Switch / MUIC Part of MAX77849 (Same as gt510wifi) ? Fuel gauge works using MAX77849 drivers
Proximity sensor Semtech SX9500 (Same as gt510wifi) Yes Missing DT bindings
GPU Adreno 306 Yes Working in kernel fork
Wi-Fi WNC3660B Yes Working in kernel fork, Using the WCN3660B compatible
Bluetooth WCN3660B Yes Working in kernel fork, Using the WCN3660B compatible
GPS Part of Modem DSP Yes Yes
Front camera (Same as gt510wifi) Siliconfile Technologies Inc. SR200PC20 Not sure, but there's a datasheet
Main camera (Same as gt510wifi) Siliconfile Technologies Inc. SR544 Old v4l2 patch for unrelated hardware, may be adaptable to current Mainline

Running some diagnostics programs on Android will likely point out some more info about sensors and any other specifications.

Patch to enable otg

The following patch modifies max77843 extcon driver for max77849 and adds support in device tree

After applying this patch the driver will not work for max77843. There are unhandled interrupts which will be disabled by linux.

Patch 

diff --git a/arch/arm64/boot/dts/qcom/msm8916-samsung-gt5-common.dtsi b/arch/arm64/boot/dts/qcom/msm8916-samsung-gt5-common.dtsi
index beb3920a83..8a69bde63e 100644
--- a/arch/arm64/boot/dts/qcom/msm8916-samsung-gt5-common.dtsi
+++ b/arch/arm64/boot/dts/qcom/msm8916-samsung-gt5-common.dtsi
@@ -117,10 +117,23 @@ fuelgauge@36 {
 		};
 	};
 
-	// FIXME: Use extcon device provided by MUIC driver when available
-	usb_vbus: usb-vbus {
-		compatible = "linux,extcon-usb-gpio";
-		vbus-gpio = <&msmgpio 2 GPIO_ACTIVE_HIGH>;
+};
+
+&blsp_i2c1 {
+	status =  "okay";
+
+	pmic@66 {
+		compatible = "maxim,max77843";
+		interrupt-parent = <&msmgpio>;
+		interrupts = <12 IRQ_TYPE_EDGE_FALLING>;
+		reg = <0x66>;
+
+		muic: max77843-muic {
+			compatible = "maxim,max77843-muic";
+
+			pinctrl-names = "default";
+			pinctrl-0 = <&muic_int_default &ovp_en_default>;
+		};
 	};
 };
 
@@ -243,12 +256,11 @@ codec {
 
 &usb {
 	status = "okay";
-	dr_mode = "peripheral";
-	extcon = <&usb_vbus>;
+	extcon = <&muic>, <&muic>;
 };
 
 &usb_hs_phy {
-	extcon = <&usb_vbus>;
+	extcon = <&muic>;
 };
 
 &wcd_codec {
@@ -412,4 +424,21 @@ jack_default: jack-default {
 		drive-strength = <2>;
 		bias-disable;
 	};
+
+	muic_int_default: muic-int-default {
+		pins = "gpio12";
+		function = "gpio";
+
+		drive-strength = <2>;
+		bias-disable;
+	};
+
+	ovp_en_default: ovp_en_default {
+		pins = "gpio102";
+		function = "gpio";
+
+		drive-strength = <2>;
+		bias-disable;
+		output-low;
+	};
 };
diff --git a/arch/arm64/configs/msm8916_defconfig b/arch/arm64/configs/msm8916_defconfig
index 8aba03f4f2..fe7bd8d87d 100644
--- a/arch/arm64/configs/msm8916_defconfig
+++ b/arch/arm64/configs/msm8916_defconfig
@@ -201,6 +201,7 @@ CONFIG_QCOM_TSENS=y
 CONFIG_QCOM_SPMI_TEMP_ALARM=y
 CONFIG_WATCHDOG=y
 CONFIG_PM8916_WATCHDOG=y
+CONFIG_MFD_MAX77843=y
 CONFIG_MFD_SPMI_PMIC=y
 CONFIG_MFD_RT5033=m
 CONFIG_REGULATOR_FIXED_VOLTAGE=y
@@ -308,6 +309,7 @@ CONFIG_QCOM_APR=m
 CONFIG_QCOM_MEMSHARE_QMI_SERVICE=m
 CONFIG_PM_DEVFREQ=y
 CONFIG_DEVFREQ_GOV_SIMPLE_ONDEMAND=y
+CONFIG_EXTCON_MAX77843=y
 CONFIG_EXTCON_SM5502=y
 CONFIG_EXTCON_USB_DUMMY=y
 CONFIG_EXTCON_USB_GPIO=y
diff --git a/drivers/extcon/extcon-max77843.c b/drivers/extcon/extcon-max77843.c
index 8e6e97ec65..6814a1967d 100644
--- a/drivers/extcon/extcon-max77843.c
+++ b/drivers/extcon/extcon-max77843.c
@@ -139,6 +139,7 @@ struct max77843_muic_irq {
 
 static struct max77843_muic_irq max77843_muic_irqs[] = {
 	{ MAX77843_MUIC_IRQ_INT1_ADC,		"MUIC-ADC" },
+	{ MAX77849_MUIC_IRQ_INT1_ADCLOW,	"MUIC-ADC_LOW" },
 	{ MAX77843_MUIC_IRQ_INT1_ADCERROR,	"MUIC-ADC_ERROR" },
 	{ MAX77843_MUIC_IRQ_INT1_ADC1K,		"MUIC-ADC1K" },
 	{ MAX77843_MUIC_IRQ_INT2_CHGTYP,	"MUIC-CHGTYP" },
@@ -146,6 +147,7 @@ static struct max77843_muic_irq max77843_muic_irqs[] = {
 	{ MAX77843_MUIC_IRQ_INT2_DCDTMR,	"MUIC-DCDTMR" },
 	{ MAX77843_MUIC_IRQ_INT2_DXOVP,		"MUIC-DXOVP" },
 	{ MAX77843_MUIC_IRQ_INT2_VBVOLT,	"MUIC-VBVOLT" },
+	{ MAX77849_MUIC_IRQ_INT2_VIDRM,		"MUIC-VIDRM" },
 	{ MAX77843_MUIC_IRQ_INT3_VBADC,		"MUIC-VBADC" },
 	{ MAX77843_MUIC_IRQ_INT3_VDNMON,	"MUIC-VDNMON" },
 	{ MAX77843_MUIC_IRQ_INT3_DNRES,		"MUIC-DNRES" },
@@ -165,6 +167,7 @@ static const struct regmap_config max77843_muic_regmap_config = {
 static const struct regmap_irq max77843_muic_irq[] = {
 	/* INT1 interrupt */
 	{ .reg_offset = 0, .mask = MAX77843_MUIC_ADC, },
+	{ .reg_offset = 0, .mask = MAX77849_MUIC_ADCLOW, },
 	{ .reg_offset = 0, .mask = MAX77843_MUIC_ADCERROR, },
 	{ .reg_offset = 0, .mask = MAX77843_MUIC_ADC1K, },
 
@@ -174,6 +177,7 @@ static const struct regmap_irq max77843_muic_irq[] = {
 	{ .reg_offset = 1, .mask = MAX77843_MUIC_DCDTMR, },
 	{ .reg_offset = 1, .mask = MAX77843_MUIC_DXOVP, },
 	{ .reg_offset = 1, .mask = MAX77843_MUIC_VBVOLT, },
+	{ .reg_offset = 1, .mask = MAX77843_MUIC_VIDRM, },
 
 	/* INT3 interrupt */
 	{ .reg_offset = 2, .mask = MAX77843_MUIC_VBADC, },
@@ -247,15 +251,12 @@ static void max77843_charger_set_otg_vbus(struct max77843_muic_info *info,
 		 bool on)
 {
 	struct max77693_dev *max77843 = info->max77843;
-	unsigned int cnfg00;
 
+	/*Fixme : Use proper registers from downstream*/
 	if (on)
-		cnfg00 = MAX77843_CHG_OTG_MASK | MAX77843_CHG_BOOST_MASK;
+		regmap_write(max77843->regmap_chg,MAX77843_CHG_REG_CHG_CNFG_00,0x2a);
 	else
-		cnfg00 = MAX77843_CHG_ENABLE | MAX77843_CHG_BUCK_MASK;
-
-	regmap_update_bits(max77843->regmap_chg, MAX77843_CHG_REG_CHG_CNFG_00,
-			   MAX77843_CHG_MODE_MASK, cnfg00);
+		regmap_write(max77843->regmap_chg,MAX77843_CHG_REG_CHG_CNFG_00,0x00); //Disable charger too
 }
 
 static int max77843_muic_get_cable_type(struct max77843_muic_info *info,
@@ -670,6 +671,7 @@ static irqreturn_t max77843_muic_irq_handler(int irq, void *data)
 
 	switch (irq_type) {
 	case MAX77843_MUIC_IRQ_INT1_ADC:
+	case MAX77849_MUIC_IRQ_INT1_ADCLOW:
 	case MAX77843_MUIC_IRQ_INT1_ADCERROR:
 	case MAX77843_MUIC_IRQ_INT1_ADC1K:
 		info->irq_adc = true;
@@ -679,6 +681,7 @@ static irqreturn_t max77843_muic_irq_handler(int irq, void *data)
 	case MAX77843_MUIC_IRQ_INT2_DCDTMR:
 	case MAX77843_MUIC_IRQ_INT2_DXOVP:
 	case MAX77843_MUIC_IRQ_INT2_VBVOLT:
+	case MAX77849_MUIC_IRQ_INT2_VIDRM:
 		info->irq_chg = true;
 		break;
 	case MAX77843_MUIC_IRQ_INT3_VBADC:
diff --git a/drivers/mfd/max77843.c b/drivers/mfd/max77843.c
index 209ee24d9c..d462d2bc0b 100644
--- a/drivers/mfd/max77843.c
+++ b/drivers/mfd/max77843.c
@@ -110,6 +110,13 @@ static int max77843_probe(struct i2c_client *i2c,
 	max77843->irq = i2c->irq;
 	max77843->type = id->driver_data;
 
+	max77843->regmap_chg = devm_regmap_init_i2c(i2c,
+			&max77843_charger_regmap_config);
+	if (IS_ERR(max77843->regmap_chg)) {
+		dev_err(&i2c->dev, "Failed to allocate register map\n");
+		return PTR_ERR(max77843->regmap_chg);
+	}
+/*
 	max77843->regmap = devm_regmap_init_i2c(i2c,
 			&max77843_regmap_config);
 	if (IS_ERR(max77843->regmap)) {
@@ -138,8 +145,20 @@ static int max77843_probe(struct i2c_client *i2c,
 		dev_err(&i2c->dev, "Failed to init Charger\n");
 		goto err_pmic_id;
 	}
+*/
+
+	/* No active discharge on safeout ldo 1,2 */
+	ret = regmap_update_bits(max77843->regmap_chg,
+				 MAX77843_SYS_REG_SAFEOUTCTRL,
+				 0x00, 0x30);
+	if (ret < 0) {
+		dev_err(&i2c->dev, "Failed to disable active discharge\n");
+	}
+
+	/* Disable charger */
+	regmap_write(max77843->regmap_chg,MAX77843_CHG_REG_CHG_CNFG_00,0x00);
 
-	ret = regmap_update_bits(max77843->regmap,
+	ret = regmap_update_bits(max77843->regmap_chg,
 				 MAX77843_SYS_REG_INTSRCMASK,
 				 MAX77843_INTSRC_MASK_MASK,
 				 (unsigned int)~MAX77843_INTSRC_MASK_MASK);
diff --git a/include/linux/mfd/max77843-private.h b/include/linux/mfd/max77843-private.h
index 0bc7454c4d..10d294e7ae 100644
--- a/include/linux/mfd/max77843-private.h
+++ b/include/linux/mfd/max77843-private.h
@@ -13,9 +13,9 @@
 #include <linux/i2c.h>
 #include <linux/regmap.h>
 
-#define I2C_ADDR_TOPSYS	(0xCC >> 1)
-#define I2C_ADDR_CHG	(0xD2 >> 1)
-#define I2C_ADDR_FG	(0x6C >> 1)
+//#define I2C_ADDR_TOPSYS	(0xCC >> 1)
+#define I2C_ADDR_CHG	(0xCC >> 1)
+//#define I2C_ADDR_FG	(0x6C >> 1)
 #define I2C_ADDR_MUIC	(0x4A >> 1)
 
 /* Topsys, Haptic and LED registers */
@@ -28,7 +28,6 @@ enum max77843_sys_reg {
 	MAX77843_SYS_REG_SYSINTSRC	= 0x24,
 	MAX77843_SYS_REG_SYSINTMASK	= 0x26,
 	MAX77843_SYS_REG_TOPSYS_STAT	= 0x28,
-	MAX77843_SYS_REG_SAFEOUTCTRL	= 0xC6,
 
 	MAX77843_SYS_REG_END,
 };
@@ -70,6 +69,7 @@ enum max77843_charger_reg {
 	MAX77843_CHG_REG_CHG_CNFG_10	= 0xC1,
 	MAX77843_CHG_REG_CHG_CNFG_11	= 0xC2,
 	MAX77843_CHG_REG_CHG_CNFG_12	= 0xC3,
+	MAX77843_SYS_REG_SAFEOUTCTRL	= 0xC6,
 
 	MAX77843_CHG_REG_END,
 };
@@ -156,6 +156,7 @@ enum max77843_irq {
 enum max77843_irq_muic {
 	/* MUIC: INT1 */
 	MAX77843_MUIC_IRQ_INT1_ADC,
+	MAX77849_MUIC_IRQ_INT1_ADCLOW,
 	MAX77843_MUIC_IRQ_INT1_ADCERROR,
 	MAX77843_MUIC_IRQ_INT1_ADC1K,
 
@@ -165,6 +166,7 @@ enum max77843_irq_muic {
 	MAX77843_MUIC_IRQ_INT2_DCDTMR,
 	MAX77843_MUIC_IRQ_INT2_DXOVP,
 	MAX77843_MUIC_IRQ_INT2_VBVOLT,
+	MAX77849_MUIC_IRQ_INT2_VIDRM,
 
 	/* MUIC: INT3 */
 	MAX77843_MUIC_IRQ_INT3_VBADC,
@@ -283,6 +285,7 @@ enum max77843_irq_muic {
 #define MAX77843_CHG_INPUT_CURRENT_LIMIT_STEP	33000
 
 #define MAX77843_MUIC_ADC			BIT(0)
+#define MAX77849_MUIC_ADCLOW		BIT(1)
 #define MAX77843_MUIC_ADCERROR			BIT(2)
 #define MAX77843_MUIC_ADC1K			BIT(3)
 
@@ -291,6 +294,7 @@ enum max77843_irq_muic {
 #define MAX77843_MUIC_DCDTMR			BIT(2)
 #define MAX77843_MUIC_DXOVP			BIT(3)
 #define MAX77843_MUIC_VBVOLT			BIT(4)
+#define MAX77843_MUIC_VIDRM				BIT(5)
 
 #define MAX77843_MUIC_VBADC			BIT(0)
 #define MAX77843_MUIC_VDNMON			BIT(1)
@@ -303,21 +307,25 @@ enum max77843_irq_muic {
 
 /* MAX77843 INTSRCMASK register */
 #define MAX77843_INTSRCMASK_CHGR		0
-#define MAX77843_INTSRCMASK_SYS			1
-#define MAX77843_INTSRCMASK_FG			2
-#define MAX77843_INTSRCMASK_MUIC		3
+#define MAX77843_INTSRCMASK_SYS			2
+//#define MAX77843_INTSRCMASK_FG			2 //not in downstream
+#define MAX77843_INTSRCMASK_MUIC		1
 
 #define MAX77843_INTSRCMASK_CHGR_MASK          BIT(MAX77843_INTSRCMASK_CHGR)
 #define MAX77843_INTSRCMASK_SYS_MASK           BIT(MAX77843_INTSRCMASK_SYS)
 #define MAX77843_INTSRCMASK_FG_MASK            BIT(MAX77843_INTSRCMASK_FG)
 #define MAX77843_INTSRCMASK_MUIC_MASK          BIT(MAX77843_INTSRCMASK_MUIC)
 
+/*Only unmask muic for now
 #define MAX77843_INTSRC_MASK_MASK \
 	(MAX77843_INTSRCMASK_MUIC_MASK | MAX77843_INTSRCMASK_FG_MASK | \
 	MAX77843_INTSRCMASK_SYS_MASK | MAX77843_INTSRCMASK_CHGR_MASK)
+*/
+#define MAX77843_INTSRC_MASK_MASK 	(MAX77843_INTSRCMASK_MUIC_MASK)
 
 /* MAX77843 STATUS register*/
 #define MAX77843_MUIC_STATUS1_ADC_SHIFT		0
+#define MAX77849_MUIC_STATUS1_ADCLOW_SHIFT		5
 #define MAX77843_MUIC_STATUS1_ADCERROR_SHIFT	6
 #define MAX77843_MUIC_STATUS1_ADC1K_SHIFT	7
 #define MAX77843_MUIC_STATUS2_CHGTYP_SHIFT	0
@@ -331,6 +339,7 @@ enum max77843_irq_muic {
 #define MAX77843_MUIC_STATUS3_MPNACK_SHIFT	6
 
 #define MAX77843_MUIC_STATUS1_ADC_MASK		(0x1f << MAX77843_MUIC_STATUS1_ADC_SHIFT)
+#define MAX77849_MUIC_STATUS1_ADCLOW_MASK	BIT(MAX77849_MUIC_STATUS1_ADCLOW_SHIFT)
 #define MAX77843_MUIC_STATUS1_ADCERROR_MASK	BIT(MAX77843_MUIC_STATUS1_ADCERROR_SHIFT)
 #define MAX77843_MUIC_STATUS1_ADC1K_MASK	BIT(MAX77843_MUIC_STATUS1_ADC1K_SHIFT)
 #define MAX77843_MUIC_STATUS2_CHGTYP_MASK	(0x7 << MAX77843_MUIC_STATUS2_CHGTYP_SHIFT)

Reference datasheets (similar devices)

Hardware / sensor status and details

Output from hwtest on SM-T350, pmos V23.12. Note that hwtest expects accelerometer units to be g, whereas the data appear to be m/s2.

hwtest

Category Model Path Status Value
framebuffer msmdrmfb /sys/class/graphics/fb0 Working U:768x1024p-0
drm /sys/class/drm/card0-DSI-1 Working 768x1024
accelerometer lis2hh12 /sys/bus/iio/devices/iio:device2 Working 5.22, 0.57, -8.17 g
vibrator gpio-vibrator /dev/input/event5 Working
input pm8941_pwrkey /dev/input/event0 Working
input pm8941_resin /dev/input/event1 Working
input GPIO Buttons /dev/input/event2 Working
input GPIO Hall Effect Sensor /dev/input/event3 Working
input Zinitix Capacitive TouchScreen /dev/input/event4 Working
input samsung-a2015 Headset Jack /dev/input/event6 Working

GPS investigation gt58wifi (SM-T350)

For overview, see Snapdragon 410/412#Modem

Test setup: pre-built image, v24.06, soc-qcom-msm8916-rproc-all, phosh/mmcli.

Location service is enumerated, 

$ qrtr-lookup 16
 Service Version Instance Node  Port
      16       2        0    0    14 Location service (~ PDS v2)

Due to "no modem", replace device /dev/modem with uri qrtr://0 (undocumented, or worse).

Location features are get/set-able, 

# qmicli -V
qmicli 1.34.0
# qmicli -d qrtr://0 --loc-get-nmea-types
Successfully retrieved NMEA types: gga, rmc, gsv, gsa, vtg, pqxfi, pstis
# qmicli -d qrtr://0 --loc-get-engine-lock
Successfully retrieved engine lock: none

But, almost any hack may work, since the api is apparently autogenerated, not designed, 

# qmicli -d qrtr://-0:anything-here! --loc-get-operation-mode
Successfully retrieved operation mode: standalone
# qmicli -d qrtr://-1 --loc-get-operation-mode
error: node with id 4294967295 not found in QRTR bus

Ignorant end-user attempts at matching Snapdragon 410/412#GNSS_(GPS) fail 

# qmicli -d qrtr://0  --loc-start --client-no-release-cid
[qrtr://0] Successfully started location tracking (session id 0)
[qrtr://0] Client ID not released:
       Service: 'loc'
           CID: '1'
# qmicli -d qrtr://0  --loc-follow-nmea --client-cid=1
error: operation failed: Unknown client 1 for service loc

"Downstream gpsd-pds" works. See arrow-db410c#Location_service_(PDS).

If you're interested in bringing up the modem/gps on APQ variants of the device, feel free to reach out to travmurav via pmOS Matrix_and_IRC channels.

See also

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