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34 To compile these devices into your kernel and use the device hints, place the
35 following lines in your kernel configuration file:
36 .Bd -ragged -offset indent
43 Additional device entries for the
46 .Bd -ragged -offset indent
49 .Cd "device imx51_gpio"
53 .Cd "device gpio_avila"
54 .Cd "device gpio_cambria"
59 Additional device entries for the
62 .Bd -ragged -offset indent
63 .Cd "device ar71xxx_gpio"
64 .Cd "device octeon_gpio"
65 .Cd "device rt305_gpio"
68 Additional device entries for the
71 .Bd -ragged -offset indent
78 system provides a simple interface to the GPIO pins that are usually
79 available on embedded architectures and can provide bit banging style
80 devices to the system.
85 .Dq General-Purpose Input/Output.
87 The BUS physically consists of multiple pins that can be configured
88 for input/output, IRQ delivery, SDA/SCL
92 On some embedded architectures (like MIPS), discovery of the bus and
93 configuration of the pins is done via
95 in the platform's kernel
99 On some others (like ARM), where
101 is used to describe the device tree, the bus discovery is done via the DTS
102 passed to the kernel, being either statically compiled in, or by a variety
103 of ways where the boot loader (or Open Firmware enabled system) passes the
104 DTS blob to the kernel at boot.
108 based system these hints can be used to configure drivers for devices
112 .Bl -tag -width ".Va hint.driver.unit.pin_list"
113 .It Va hint.driver.unit.at
116 where the device is attached.
122 are the driver name and the unit number for the device driver.
123 .It Va hint.driver.unit.pins
124 This is a bitmask of the pins on the
126 that are connected to the device.
127 The pins will be allocated to the specified driver instance.
128 Only pins with numbers from 0 to 31 can be specified using this hint.
129 .It Va hint.driver.unit.pin_list
130 This is a list of pin numbers of pins on the
132 that are connected to the device.
133 The pins will be allocated to the specified driver instance.
134 This is a more user friendly alternative to the
137 Additionally, this hint allows specifying pin numbers greater than 31.
138 The numbers can be decimal or hexadecimal with 0x prefix.
139 Any non-digit character can be used as a separator.
140 For example, it can be a comma, a slash or a space.
141 The separator can be followed by any number of space characters.
146 are only provided by the
149 .Bl -tag -width ".Va hint.gpio.function_clear"
150 .It Va hint.gpio.%d.pinmask
151 This is a bitmask of pins on the GPIO board that we would like to expose
152 for use to the host operating system.
153 To expose pin 0, 4 and 7, use the bitmask of
154 10010001 converted to the hexadecimal value 0x0091.
155 .It Va hint.gpio.%d.pinon
156 This is a bitmask of pins on the GPIO board that will be set to ON at host
158 To set pin 2, 5 and 13 to be set ON at boot, use the bitmask of
159 10000000010010 converted to the hexadecimal value 0x2012.
160 .It Va hint.gpio.function_set
161 .It Va hint.gpio.function_clear
162 These are bitmasks of pins that will remap a pin to handle a specific
163 function (USB, UART TX/RX, etc) in the Atheros function registers.
164 This is mainly used to set/clear functions that we need when they are set up or
168 Simply put, each pin of the GPIO interface is connected to an input/output
169 of some device in a system.
179 manual page first appeared in
183 manual page was written by
184 .An Sean Bruno Aq Mt sbruno@FreeBSD.org .