| | 40 | |
| | 41 | == UART Information for GW73xx |
| | 42 | |
| | 43 | The UART3 (/dev/ttymxc2) on J10 on a GW73xx board is shared with the onboard Bluetooth module. |
| | 44 | |
| | 45 | This is defined in the device tree here: |
| | 46 | [https://github.com/Gateworks/linux-venice/blob/v5.15.15-venice/arch/arm64/boot/dts/freescale/imx8mm-venice-gw73xx.dtsi#L218] |
| | 47 | |
| | 48 | {{{ |
| | 49 | /* bluetooth HCI */ |
| | 50 | &uart3 { |
| | 51 | pinctrl-names = "default"; |
| | 52 | pinctrl-0 = <&pinctrl_uart3>, <&pinctrl_bten>; |
| | 53 | cts-gpios = <&gpio5 8 GPIO_ACTIVE_LOW>; |
| | 54 | rts-gpios = <&gpio5 9 GPIO_ACTIVE_LOW>; |
| | 55 | status = "okay"; |
| | 56 | |
| | 57 | bluetooth { |
| | 58 | compatible = "brcm,bcm4330-bt"; |
| | 59 | shutdown-gpios = <&gpio1 3 GPIO_ACTIVE_HIGH>; |
| | 60 | }; |
| | 61 | }; |
| | 62 | |
| | 63 | }}} |
| | 64 | |
| | 65 | To understand this better, think of how it works: UART devices don't have any sort of magic device 'auto-detection' like enumerated busses such as PCI and USB do (which have a bus infrastructure to provide things like a class, manufacturer, and device ID). Therefore device-tree must be used to explain to the OS what is there and map it to a driver. This is what the 'compatible = "brcm,bcm4330-bt"' string does; there is a driver that matches that compatible string. |
| | 66 | |
| | 67 | It is possible to not see a /dev/ttymxc2 corresponding to schematic UART3 (NXP references hardware blocks as 1 based, Linux references them as 0 based) is indeed because the bluetooth HCI driver (hci_bcm) claims the UART such that Linux removes access from it to not conflict with it. The 'hci_bcm' driver won't fail to recognize the UART (ie if on a GW7300 which doesn't load that part) and remove it's claim on the device. Gateworks will not typically try to do things like removing that dynamically in the boot firmware via a dt fixup based on the model (because mapping model strings to what parts are loaded is a really bad idea). |
| | 68 | |
| | 69 | To remedy this, one can either comment out the 'bluetooth' node in the device-tree if using a custom kernel/dt or use a 'fix_fdt' script. |
| | 70 | |
| | 71 | - In Linux find the device path |
| | 72 | {{{ |
| | 73 | # find /proc/device-tree/ -name "bluetooth" |
| | 74 | /proc/device-tree/soc@0/bus@30800000/spba-bus@30800000/serial@30880000/bluetooth |
| | 75 | }}} |
| | 76 | |
| | 77 | - In U-Boot create a fixfdt script as documented on our wiki [http://trac.gateworks.com/wiki/linux/devicetree#fixfdtscript] |
| | 78 | {{{ |
| | 79 | u-boot=> setenv fixfdt 'fdt addr $fdt_addr_r; fdt resize; fdt set /soc@0/bus@30800000/spba-bus@30800000/serial@30880000/bluetooth status disabled' |
| | 80 | }}} |
| | 81 | |
| | 82 | If the V2X support requires a kernel driver then it will need a device-tree binding of its own in which case one can use a dt overlay or customize the device tree. |
