The BeagleBoard.org PocketBeagle has P1 and P2 headers [0] which expose
many of the TI AM3358 SoC balls to stacking expansion boards called
"capes", or to other external connections like jumper wires connected
to a breadboard.

Note: the AM3358 die is actually embedded inside of the OSD335x-SM
System-in-Package (SiP) [1] but that is irrelevant to the gpio driver.

Many of the P1 and P2 header pins can muxed to a GPIO line.  The
gpio-line-names describe which P1 or P2 pin that line goes to and the
default mux for that P1 or P2 pin if it is not GPIO.

Some GPIO lines are named "[NC]" as the corresponding balls are not
routed to anything on the PCB.

The goal for these names is to make it easier for a user viewing the
output of gpioinfo to determine which P1 or P2 pin is connected to a
GPIO line.  The output of gpioinfo on a PocketBeagle would be:

gpiochip0 - 32 lines:
	line   0:       "[NC]"       unused   input  active-high
	line   1:       "[NC]"       unused   input  active-high
	line   2: "P1.08 [SPI0_CLK]" unused input active-high
	line   3: "P1.10 [SPI0_MISO]" unused input active-high
	line   4: "P1.12 [SPI0_MOSI]" unused input active-high
	line   5: "P1.06 [SPI0_CS]" unused input active-high
	line   6:  "[MMC0_CD]"         "cd"   input   active-low [used]
	line   7: "P2.29 [SPI1_CLK]" unused input active-high
	line   8:  "[SYSBOOT]"       unused   input  active-high
	line   9:  "[SYSBOOT]"       unused   input  active-high
	line  10:  "[SYSBOOT]"       unused   input  active-high
	line  11:  "[SYSBOOT]"       unused   input  active-high
	line  12: "P1.26 [I2C2_SDA]" unused input active-high
	line  13: "P1.28 [I2C2_SCL]" unused input active-high
	line  14: "P2.11 [I2C1_SDA]" unused input active-high
	line  15: "P2.09 [I2C1_SCL]" unused input active-high
	line  16:       "[NC]"       unused   input  active-high
	line  17:       "[NC]"       unused   input  active-high
	line  18:       "[NC]"       unused   input  active-high
	line  19: "P2.31 [SPI1_CS]" unused input active-high
	line  20: "P1.20 [PRU0.16]" unused input active-high
	line  21:       "[NC]"       unused   input  active-high
	line  22:       "[NC]"       unused   input  active-high
	line  23:      "P2.03"       unused   input  active-high
	line  24:       "[NC]"       unused   input  active-high
	line  25:       "[NC]"       unused   input  active-high
	line  26:      "P1.34"       unused   input  active-high
	line  27:      "P2.19"       unused   input  active-high
	line  28:       "[NC]"       unused   input  active-high
	line  29:       "[NC]"       unused   input  active-high
	line  30: "P2.05 [UART4_RX]" unused input active-high
	line  31: "P2.07 [UART4_TX]" unused input active-high
gpiochip1 - 32 lines:
	line   0:       "[NC]"       unused   input  active-high
	line   1:       "[NC]"       unused   input  active-high
	line   2:       "[NC]"       unused   input  active-high
	line   3:       "[NC]"       unused   input  active-high
	line   4:       "[NC]"       unused   input  active-high
	line   5:       "[NC]"       unused   input  active-high
	line   6:       "[NC]"       unused   input  active-high
	line   7:       "[NC]"       unused   input  active-high
	line   8:       "[NC]"       unused   input  active-high
	line   9: "P2.25 [SPI1_MOSI]" unused input active-high
	line  10: "P1.32 [UART0_RX]" unused input active-high
	line  11: "P1.30 [UART0_TX]" unused input active-high
	line  12:      "P2.24"       unused   input  active-high
	line  13:      "P2.33"       unused   input  active-high
	line  14:      "P2.22"       unused   input  active-high
	line  15:      "P2.18"       unused   input  active-high
	line  16:       "[NC]"       unused   input  active-high
	line  17:       "[NC]"       unused   input  active-high
	line  18: "P2.01 [PWM1A]" unused input active-high
	line  19:       "[NC]"       unused   input  active-high
	line  20:      "P2.10"       unused   input  active-high
	line  21: "[USR LED 0]" "beaglebone:green:usr0" output active-high [used]
	line  22: "[USR LED 1]" "beaglebone:green:usr1" output active-high [used]
	line  23: "[USR LED 2]" "beaglebone:green:usr2" output active-high [used]
	line  24: "[USR LED 3]" "beaglebone:green:usr3" output active-high [used]
	line  25:      "P2.06"       unused   input  active-high
	line  26:      "P2.04"       unused   input  active-high
	line  27:      "P2.02"       unused   input  active-high
	line  28:      "P2.08"       unused   input  active-high
	line  29:       "[NC]"       unused   input  active-high
	line  30:       "[NC]"       unused   input  active-high
	line  31:       "[NC]"       unused   input  active-high
gpiochip2 - 32 lines:
	line   0:      "P2.20"       unused   input  active-high
	line   1:      "P2.17"       unused   input  active-high
	line   2:       "[NC]"       unused   input  active-high
	line   3:       "[NC]"       unused   input  active-high
	line   4:       "[NC]"       unused   input  active-high
	line   5: "[EEPROM_WP]" unused input active-high
	line   6:  "[SYSBOOT]"       unused   input  active-high
	line   7:  "[SYSBOOT]"       unused   input  active-high
	line   8:  "[SYSBOOT]"       unused   input  active-high
	line   9:  "[SYSBOOT]"       unused   input  active-high
	line  10:  "[SYSBOOT]"       unused   input  active-high
	line  11:  "[SYSBOOT]"       unused   input  active-high
	line  12:  "[SYSBOOT]"       unused   input  active-high
	line  13:  "[SYSBOOT]"       unused   input  active-high
	line  14:  "[SYSBOOT]"       unused   input  active-high
	line  15:  "[SYSBOOT]"       unused   input  active-high
	line  16:  "[SYSBOOT]"       unused   input  active-high
	line  17:  "[SYSBOOT]"       unused   input  active-high
	line  18:       "[NC]"       unused   input  active-high
	line  19:       "[NC]"       unused   input  active-high
	line  20:       "[NC]"       unused   input  active-high
	line  21:       "[NC]"       unused   input  active-high
	line  22: "P2.35 [AIN5]" unused input active-high
	line  23: "P1.02 [AIN6]" unused input active-high
	line  24: "P1.35 [PRU1.10]" unused input active-high
	line  25: "P1.04 [PRU1.11]" unused input active-high
	line  26: "[MMC0_DAT3]" unused input active-high
	line  27: "[MMC0_DAT2]" unused input active-high
	line  28: "[MMC0_DAT1]" unused input active-high
	line  29: "[MMC0_DAT0]" unused input active-high
	line  30: "[MMC0_CLK]"       unused   input  active-high
	line  31: "[MMC0_CMD]"       unused   input  active-high
gpiochip3 - 32 lines:
	line   0:       "[NC]"       unused   input  active-high
	line   1:       "[NC]"       unused   input  active-high
	line   2:       "[NC]"       unused   input  active-high
	line   3:       "[NC]"       unused   input  active-high
	line   4:       "[NC]"       unused   input  active-high
	line   5: "[I2C0_SDA]"       unused   input  active-high
	line   6: "[I2C0_SCL]"       unused   input  active-high
	line   7:     "[JTAG]"       unused   input  active-high
	line   8:     "[JTAG]"       unused   input  active-high
	line   9:       "[NC]"       unused   input  active-high
	line  10:       "[NC]"       unused   input  active-high
	line  11:       "[NC]"       unused   input  active-high
	line  12:       "[NC]"       unused   input  active-high
	line  13: "P1.03 [USB1]" unused input active-high
	line  14: "P1.36 [PWM0A]" unused input active-high
	line  15: "P1.33 [PRU0.1]" unused input active-high
	line  16: "P2.32 [PRU0.2]" unused input active-high
	line  17: "P2.30 [PRU0.3]" unused input active-high
	line  18: "P1.31 [PRU0.4]" unused input active-high
	line  19: "P2.34 [PRU0.5]" unused input active-high
	line  20: "P2.28 [PRU0.6]" unused input active-high
	line  21: "P1.29 [PRU0.7]" unused input active-high
	line  22:       "[NC]"       unused   input  active-high
	line  23:       "[NC]"       unused   input  active-high
	line  24:       "[NC]"       unused   input  active-high
	line  25:       "[NC]"       unused   input  active-high
	line  26:       "[NC]"       unused   input  active-high
	line  27:       "[NC]"       unused   input  active-high
	line  28:       "[NC]"       unused   input  active-high
	line  29:       "[NC]"       unused   input  active-high
	line  30:       "[NC]"       unused   input  active-high
	line  31:       "[NC]"       unused   input  active-high

[0] https://github.com/beagleboard/pocketbeagle/wiki/System-Reference-Manual#71_Expansion_Header_Connectors
[1] https://octavosystems.com/app_notes/osd335x-family-pin-assignments/Reviewed-by: Jason Kridner <jason@beagleboard.org>
Reviewed-by: Robert Nelson <robertcnelson@gmail.com>
Signed-off-by: Drew Fustini <drew@beagleboard.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>