Hi, I'm using the GPIO driver gpio-mcp23s08 for two MCP23S17 chips that use the same SPI chip select (and different addresses). My device tree contains: &spi0 { status = "okay"; bus-num = <0>; num-cs = <2>; cs-gpios = <&portc 2 0>, <&portc 3 0>; gpio@1 { compatible = "microchip,mcp23s17"; gpio-controller; #gpio-cells = <2>; microchip,spi-present-mask = <0x03>; reg = <1>; spi-max-frequency = <1000000>; }; }; Both gpiochips are registered and I can see them in /sys/class/gpio as gpiochip395 and gpiochip411. My problem is that I can't figure out which gpiochip is which. They both have the same label, ngpio and share the same of_node. Setting some GPIOs and probing the hardware helped me determine that gpiochip411 was the chip with addr = 0 and gpiochip395 was the chip with addr = 1. However I presume there is no guarantee on what base number is allocated to each chip? In fact, if I repeatedly unload and reload the driver each time the base numbers decrease until I eventually get the following warning: [ 3376.068639] gpiochip_find_base: cannot find free range [ 3376.073766] gpiochip_add_data: GPIOs 0..15 (mcp23s17) failed to register [ 3376.080474] ------------[ cut here ]------------ [ 3376.085105] WARNING: CPU: 1 PID: 807 at drivers/base/core.c:251 device_release+0x8c/0x90 [ 3376.093159] Device 'gpiochip29' does not have a release() function, it is broken and must be fixed. [ 3376.102174] Modules linked in: gpio_mcp23s08(+) [last unloaded: gpio_mcp23s08] [ 3376.109420] CPU: 1 PID: 807 Comm: modprobe Not tainted 4.7.0-rc2 #10 [ 3376.115744] Hardware name: Altera SOCFPGA [ 3376.119766] [<c010f780>] (unwind_backtrace) from [<c010b864>] (show_stack+0x10/0x14) [ 3376.127487] [<c010b864>] (show_stack) from [<c02c20f8>] (dump_stack+0x8c/0xa0) [ 3376.134685] [<c02c20f8>] (dump_stack) from [<c011c434>] (__warn+0xec/0x104) [ 3376.141619] [<c011c434>] (__warn) from [<c011c484>] (warn_slowpath_fmt+0x38/0x48) [ 3376.149074] [<c011c484>] (warn_slowpath_fmt) from [<c0324798>] (device_release+0x8c/0x90) [ 3376.157223] [<c0324798>] (device_release) from [<c02c40e0>] (kobject_put+0xb4/0xec) [ 3376.164858] [<c02c40e0>] (kobject_put) from [<bf04ef74>] (mcp23s08_probe+0x2c0/0x318 [gpio_mcp23s08]) [ 3376.174055] [<bf04ef74>] (mcp23s08_probe [gpio_mcp23s08]) from [<c035b7c8>] (spi_drv_probe+0x7c/0xa8) [ 3376.183245] [<c035b7c8>] (spi_drv_probe) from [<c0328be0>] (driver_probe_device+0x224/0x2bc) [ 3376.191653] [<c0328be0>] (driver_probe_device) from [<c0328d30>] (__driver_attach+0xb8/0xbc) [ 3376.200057] [<c0328d30>] (__driver_attach) from [<c0326f18>] (bus_for_each_dev+0x68/0x9c) [ 3376.208203] [<c0326f18>] (bus_for_each_dev) from [<c0328068>] (bus_add_driver+0x1a4/0x21c) [ 3376.216437] [<c0328068>] (bus_add_driver) from [<c0329694>] (driver_register+0x78/0xf8) [ 3376.224414] [<c0329694>] (driver_register) from [<bf052014>] (init_module+0x14/0x50 [gpio_mcp23s08]) [ 3376.233513] [<bf052014>] (init_module [gpio_mcp23s08]) from [<c0101780>] (do_one_initcall+0x40/0x174) [ 3376.242698] [<c0101780>] (do_one_initcall) from [<c01c9c50>] (do_init_module+0x64/0x394) [ 3376.250763] [<c01c9c50>] (do_init_module) from [<c018ceb4>] (load_module+0x1a60/0x206c) [ 3376.258736] [<c018ceb4>] (load_module) from [<c018d60c>] (SyS_init_module+0x14c/0x15c) [ 3376.266624] [<c018d60c>] (SyS_init_module) from [<c0107680>] (ret_fast_syscall+0x0/0x3c) [ 3376.274700] ---[ end trace 3a4ba228e00948b3 ]--- [ 3376.279316] mcp23s08: probe of spi0.1 failed with error -28 Ultimately I'd like to be able to use gpio-line-names in the device tree to name each of the GPIOs I'll be using in user space. To support multiple chips on the same SPI chip select I came up with this patch: --- a/drivers/gpio/gpio-mcp23s08.c +++ b/drivers/gpio/gpio-mcp23s08.c @@ -552,6 +552,7 @@ static int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev, { int status; bool mirror = false; + struct device_node *np; mutex_init(&mcp->lock); @@ -566,7 +567,24 @@ static int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev, mcp->chip.dbg_show = mcp23s08_dbg_show; #ifdef CONFIG_OF mcp->chip.of_gpio_n_cells = 2; - mcp->chip.of_node = dev->of_node; + for_each_child_of_node(dev->of_node, np) { + const __be32 *reg; + int len; + int a_cells, s_cells; + + reg = of_get_property(np, "reg", &len); + if (!reg) + continue; + + a_cells = of_n_addr_cells(np); + s_cells = of_n_size_cells(np); + + if (of_read_number(reg, a_cells) == cs) { + mcp->chip.of_node = np; + } + } + if (!mcp->chip.of_node) + mcp->chip.of_node = dev->of_node; #endif switch (type) { This allows me to use something like this in my device tree: gpio@1 { compatible = "microchip,mcp23s17"; gpio-controller; #gpio-cells = <2>; microchip,spi-present-mask = <0x03>; reg = <1>; spi-max-frequency = <1000000>; chip@0 { reg = <0>; gpio-line-names = "RLY_CTRL3", /* GPA0 */ ... chip@1 { reg = <1>; gpio-line-names = "USBA_PWR", /* GPA0 */ ... Which displays the names correctly with lsgpio, however I'm still stuck on how to figure out which base number to use when I want to export one of these GPIOs. Regards, Nathan