前言：

解决usb虚拟u盘无法probe驱动的问题--Apple的学习笔记之前已经玩了下usb，但是我认为方便不正确，我是通过对比tisdk的打印信息来找线索，对usb文件夹中的c文件含义并不是很清楚。所以今天来一次相对正式方法来学习。之前直接编译入内核，这次改成模块加载方式。

一，usb子系统结构

1，底层控制器+phy驱动(通过设备树可以看到usb分为5个匹配项)
modprobe musb_am335x(注册usb设备)
modprobe phy-am335x(注册usb控制器和phy)
modprobe musb_dsps(驱动，用来匹配底层设备)
2，usb总线协议
modprobe usbcore(注册总线及协议)
3，上层应用协议(串口，虚拟网卡，u盘等)
modprobe udc-core(上层协议的中间件)

二，过程中的问题

通过添加模块的方法居然无法创建/sys/class/udc下面的设备
解决方法:
设备树搜索，发现musb_am335x.c是需要被调用的，否则无法匹配设备树。但是我对比.config将y改成M的呀，都没有搜索到CONFIG_USB_MUSB_AM335X_CHILD呀？原来CONFIG_USB_MUSB_AM335X_CHILD是tristate属性的，所以被隐藏了。由于我之前CONFIG_USB_MUSB_DSPS选择为y，所以CONFIG_USB_MUSB_AM335X_CHILD就自动变成y。

2. 添加modprobe musb_am335x后能创建musb-hdrc.0的设备。

三，关于musb-hdrc设备匹配的理解

因为现在设备树用多，所以任何的匹配我都会去dts中找，所以我搜索musb-hdrc，没有搜索到。那么只能去分析代码。后来发现
dsps_probe->platform_device_alloc("musb-hdrc"...)所以关于musb-hdrc的匹配是通过driver_match_device函数中的dev.name来匹配的。

四，最后成功

只要musb-hdrc.0能创建出来，usb虚拟U盘就能成功。

Welcome to Buildroot
buildroot login: root
# modprobe musb_am335x
# modprobe phy-am335x
[   21.566063] am335x-phy-driver 47401300.usb-phy: GPIO lookup for consumer reset
[   21.573584] am335x-phy-driver 47401300.usb-phy: using device tree for GPIO lookup
[   21.581152] of_get_named_gpiod_flags: can't parse 'reset-gpios' property of node '/ocp/usb@47400000/usb-phy@47401300[0]'
[   21.592151] of_get_named_gpiod_flags: can't parse 'reset-gpio' property of node '/ocp/usb@47400000/usb-phy@47401300[0]'
[   21.603026] am335x-phy-driver 47401300.usb-phy: using lookup tables for GPIO lookup
[   21.610725] am335x-phy-driver 47401300.usb-phy: No GPIO consumer reset found
[   21.617835] am335x-phy-driver 47401300.usb-phy: GPIO lookup for consumer vbus-detect
[   21.625640] am335x-phy-driver 47401300.usb-phy: using device tree for GPIO lookup
[   21.633202] of_get_named_gpiod_flags: can't parse 'vbus-detect-gpios' property of node '/ocp/usb@47400000/usb-phy@47401300[0]'
[   21.644686] of_get_named_gpiod_flags: can't parse 'vbus-detect-gpio' property of node '/ocp/usb@47400000/usb-phy@47401300[0]'
[   21.656072] am335x-phy-driver 47401300.usb-phy: using lookup tables for GPIO lookup
[   21.663788] am335x-phy-driver 47401300.usb-phy: No GPIO consumer vbus-detect found
[   21.671535] am335x-phy-driver 47401300.usb-phy: 47401300.usb-phy supply vcc not found, using dummy regulator
[   21.686799] am335x-phy-driver 47401b00.usb-phy: GPIO lookup for consumer reset
[   21.694279] am335x-phy-driver 47401b00.usb-phy: using device tree for GPIO lookup
[   21.701845] of_get_named_gpiod_flags: can't parse 'reset-gpios' property of node '/ocp/usb@47400000/usb-phy@47401b00[0]'
[   21.712863] of_get_named_gpiod_flags: can't parse 'reset-gpio' property of node '/ocp/usb@47400000/usb-phy@47401b00[0]'
[   21.723742] am335x-phy-driver 47401b00.usb-phy: using lookup tables for GPIO lookup
[   21.731442] am335x-phy-driver 47401b00.usb-phy: No GPIO consumer reset found
[   21.738556] am335x-phy-driver 47401b00.usb-phy: GPIO lookup for consumer vbus-detect
[   21.746364] am335x-phy-driver 47401b00.usb-phy: using device tree for GPIO lookup
[   21.753930] of_get_named_gpiod_flags: can't parse 'vbus-detect-gpios' property of node '/ocp/usb@47400000/usb-phy@47401b00[0]'
[   21.765420] of_get_named_gpiod_flags: can't parse 'vbus-detect-gpio' property of node '/ocp/usb@47400000/usb-phy@47401b00[0]'
[   21.776809] am335x-phy-driver 47401b00.usb-phy: using lookup tables for GPIO lookup
[   21.784529] am335x-phy-driver 47401b00.usb-phy: No GPIO consumer vbus-detect found
[   21.792274] am335x-phy-driver 47401b00.usb-phy: 47401b00.usb-phy supply vcc not found, using dummy regulator
# modprobe usbcore
[   28.904523] usbcore: registered new interface driver usbfs
[   28.910148] usbcore: registered new interface driver hub
[   28.915736] usbcore: registered new device driver usb
# modprobe musb_hdrc
# modprobe udc-core
# modprobe musb_dsps
[   42.281548] musb-dsps 47401400.usb: VBUS irq 59 configured
[   42.288197] go musb_probe
[   42.290896] go musb_init_controller
[   42.299794] musb-hdrc: ConfigData=0xde (UTMI-8, dyn FIFOs, bulk combine, bulk split, HB-ISO Rx, HB-ISO Tx, SoftConn)
[   42.310442] musb-hdrc: MHDRC RTL version 2.0
[   42.314764] musb-hdrc: setup fifo_mode 4
[   42.318722] musb-hdrc: 28/31 max ep, 16384/16384 memory
[   42.324334] musb->port_mode is 2
[   42.324340] go musb_gadget_setup
[   42.330860] go usb_add_gadget_udc
[   42.334243] go usb_add_gadget_udc_release
[   42.339802] go musb_probe
[   42.342502] go musb_init_controller
[   42.351315] musb-hdrc: ConfigData=0xde (UTMI-8, dyn FIFOs, bulk combine, bulk split, HB-ISO Rx, HB-ISO Tx, SoftConn)
[   42.361956] musb-hdrc: MHDRC RTL version 2.0
[   42.366275] musb-hdrc: setup fifo_mode 4
[   42.370231] musb-hdrc: 28/31 max ep, 16384/16384 memory
# ls /sys/class/udc
musb-hdrc.0
# lsmod
Module                  Size  Used by    Not tainted
musb_dsps              20480  0 
musb_hdrc              86016  1 musb_dsps
udc_core               40960  1 musb_hdrc
usbcore               200704  0 
phy_am335x             16384  2 
phy_am335x_control     16384  1 phy_am335x
phy_generic            16384  1 phy_am335x
usb_common             16384  5 musb_dsps,musb_hdrc,udc_core,usbcore,phy_am335x
musb_am335x            16384  0 [permanent]
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