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32 To compile these devices into your kernel and use the device hints, place the
33 following lines in your kernel configuration file:
34 .Bd -ragged -offset indent
41 Additional device entries for the
44 .Bd -ragged -offset indent
47 .Cd "device imx51_gpio"
51 .Cd "device gpio_avila"
52 .Cd "device gpio_cambria"
57 Additional device entries for the
60 .Bd -ragged -offset indent
61 .Cd "device ar71xxx_gpio"
62 .Cd "device octeon_gpio"
63 .Cd "device rt305_gpio"
66 Additional device entries for the
69 .Bd -ragged -offset indent
74 Additional device entries for the
77 .Bd -ragged -offset indent
78 .Cd "device sifive_gpio"
83 system provides a simple interface to the GPIO pins that are usually
84 available on embedded architectures and can provide bit banging style
85 devices to the system.
90 .Dq General-Purpose Input/Output.
92 The BUS physically consists of multiple pins that can be configured
93 for input/output, IRQ delivery, SDA/SCL
97 On some embedded architectures (like MIPS), discovery of the bus and
98 configuration of the pins is done via
100 in the platform's kernel
104 On some others (like ARM), where
106 is used to describe the device tree, the bus discovery is done via the DTS
107 passed to the kernel, being either statically compiled in, or by a variety
108 of ways where the boot loader (or Open Firmware enabled system) passes the
109 DTS blob to the kernel at boot.
113 based system these hints can be used to configure drivers for devices
117 .Bl -tag -width ".Va hint.driver.unit.pin_list"
118 .It Va hint.driver.unit.at
121 where the device is attached.
127 are the driver name and the unit number for the device driver.
128 .It Va hint.driver.unit.pins
129 This is a bitmask of the pins on the
131 that are connected to the device.
132 The pins will be allocated to the specified driver instance.
133 Only pins with numbers from 0 to 31 can be specified using this hint.
134 .It Va hint.driver.unit.pin_list
135 This is a list of pin numbers of pins on the
137 that are connected to the device.
138 The pins will be allocated to the specified driver instance.
139 This is a more user friendly alternative to the
142 Additionally, this hint allows specifying pin numbers greater than 31.
143 The numbers can be decimal or hexadecimal with 0x prefix.
144 Any non-digit character can be used as a separator.
145 For example, it can be a comma, a slash or a space.
146 The separator can be followed by any number of space characters.
151 are only provided by the
154 .Bl -tag -width ".Va hint.gpio.function_clear"
155 .It Va hint.gpio.%d.pinmask
156 This is a bitmask of pins on the GPIO board that we would like to expose
157 for use to the host operating system.
158 To expose pin 0, 4 and 7, use the bitmask of
159 10010001 converted to the hexadecimal value 0x0091.
160 .It Va hint.gpio.%d.pinon
161 This is a bitmask of pins on the GPIO board that will be set to ON at host
163 To set pin 2, 5 and 13 to be set ON at boot, use the bitmask of
164 10000000010010 converted to the hexadecimal value 0x2012.
165 .It Va hint.gpio.function_set
166 .It Va hint.gpio.function_clear
167 These are bitmasks of pins that will remap a pin to handle a specific
168 function (USB, UART TX/RX, etc) in the Atheros function registers.
169 This is mainly used to set/clear functions that we need when they are set up or
173 Simply put, each pin of the GPIO interface is connected to an input/output
174 of some device in a system.
184 manual page first appeared in
188 manual page was written by
189 .An Sean Bruno Aq Mt sbruno@FreeBSD.org .