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看了一篇文章《debug by printing》,文中提到了多种通过printk来调试驱动的方法，其中最有用的就是"Dynamic debugging"。
“Dynamic debugging"的官方文档：http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/dynamic-debug-howto.txt?id=HEAD
"Dyanmic debugging"的功能适用于所有的linux内核，所以也可以用于嵌入式开发板中调试驱动程序。
在使用"Dynamic debugging"前需要在内核中使能Dynamic printk选项（可用于控制代码代码中的pr_debug和dev_dbg的信息是否输出）。
默认官方debian内核中没有使能这个选项，可以参考我的博文《debian下配置dynamic printk以及重新编译内核 》重新编译和配置内核才能使用该功能。
本文用一个usb转串口线（核心芯片是pl2303）的例子来说明如何使用"Dynamic debugging"，内核版本是linux-3.2.57。
先插入usb转串口线，得到下面的信息：
[ 8.728526] usbcore: registered new interface driver usbserial
[ 8.728669] USB Serial support registered for generic
[ 8.728720] usbcore: registered new interface driver usbserial_generic
[ 8.728722] usbserial: USB Serial Driver core
[ 8.737942] USB Serial support registered for pl2303
[ 8.737963] pl2303 5-2:1.0: pl2303 converter detected
[ 8.750530] usb 5-2: pl2303 converter now attached to ttyUSB0
[ 8.750565] usbcore: registered new interface driver pl2303
[ 8.750568] pl2303: Prolific PL2303 USB to serial adaptor driver
pl2303驱动中用到了pl2303的驱动，查看pl2303驱动信息：
$ sudo modinfo pl2303 filename: /lib/modules/3.2.57/kernel/drivers/usb/serial/pl2303.ko license: GPL description: Prolific PL2303 USB to serial adaptor driver alias: usb:v0B8Cp2303d*dc*dsc*dp*ic*isc*ip* alias: usb:v0B63p6530d*dc*dsc*dp*ic*isc*ip* alias: usb:v11ADp0001d*dc*dsc*dp*ic*isc*ip* alias: usb:v054Cp0437d*dc*dsc*dp*ic*isc*ip* alias: usb:v04B8p0522d*dc*dsc*dp*ic*isc*ip* alias: usb:v04B8p0521d*dc*dsc*dp*ic*isc*ip* alias: usb:v03F0p3524d*dc*dsc*dp*ic*isc*ip* alias: usb:v5372p2303d*dc*dsc*dp*ic*isc*ip* alias: usb:v05ADp0FBAd*dc*dsc*dp*ic*isc*ip* alias: usb:v07AAp002Ad*dc*dsc*dp*ic*isc*ip* alias: usb:v11F6p2001d*dc*dsc*dp*ic*isc*ip* alias: usb:v058Fp9720d*dc*dsc*dp*ic*isc*ip* alias: usb:v050Dp0257d*dc*dsc*dp*ic*isc*ip* alias: usb:v0731p2003d*dc*dsc*dp*ic*isc*ip* alias: usb:v0E55p110Bd*dc*dsc*dp*ic*isc*ip* alias: usb:v0413p2101d*dc*dsc*dp*ic*isc*ip* alias: usb:v079Bp0027d*dc*dsc*dp*ic*isc*ip* alias: usb:v10B5pAC70d*dc*dsc*dp*ic*isc*ip* alias: usb:v078Bp1234d*dc*dsc*dp*ic*isc*ip* alias: usb:v0745p0001d*dc*dsc*dp*ic*isc*ip* alias: usb:v04A5p4027d*dc*dsc*dp*ic*isc*ip* alias: usb:v11F5p0005d*dc*dsc*dp*ic*isc*ip* alias: usb:v11F5p0004d*dc*dsc*dp*ic*isc*ip* alias: usb:v11F5p0003d*dc*dsc*dp*ic*isc*ip* alias: usb:v11F5p0001d*dc*dsc*dp*ic*isc*ip* alias: usb:v04E8p8001d*dc*dsc*dp*ic*isc*ip* alias: usb:v11F7p02DFd*dc*dsc*dp*ic*isc*ip* alias: usb:v6189p2068d*dc*dsc*dp*ic*isc*ip* alias: usb:v0731p0528d*dc*dsc*dp*ic*isc*ip* alias: usb:v1453p4026d*dc*dsc*dp*ic*isc*ip* alias: usb:v2478p2008d*dc*dsc*dp*ic*isc*ip* alias: usb:v0584pB000d*dc*dsc*dp*ic*isc*ip* alias: usb:v0DF7p0620d*dc*dsc*dp*ic*isc*ip* alias: usb:v0EBAp2080d*dc*dsc*dp*ic*isc*ip* alias: usb:v0EBAp1080d*dc*dsc*dp*ic*isc*ip* alias: usb:v056Ep5004d*dc*dsc*dp*ic*isc*ip* alias: usb:v056Ep5003d*dc*dsc*dp*ic*isc*ip* alias: usb:v0547p2008d*dc*dsc*dp*ic*isc*ip* alias: usb:v0557p2008d*dc*dsc*dp*ic*isc*ip* alias: usb:v04BBp0A0Ed*dc*dsc*dp*ic*isc*ip* alias: usb:v04BBp0A03d*dc*dsc*dp*ic*isc*ip* alias: usb:v067Bp0307d*dc*dsc*dp*ic*isc*ip* alias: usb:v067Bp331Ad*dc*dsc*dp*ic*isc*ip* alias: usb:v067Bp0609d*dc*dsc*dp*ic*isc*ip* alias: usb:v067Bp0612d*dc*dsc*dp*ic*isc*ip* alias: usb:v067Bp0611d*dc*dsc*dp*ic*isc*ip* alias: usb:v067BpAAA0d*dc*dsc*dp*ic*isc*ip* alias: usb:v067BpAAA2d*dc*dsc*dp*ic*isc*ip* alias: usb:v067Bp1234d*dc*dsc*dp*ic*isc*ip* alias: usb:v067Bp04BBd*dc*dsc*dp*ic*isc*ip* alias: usb:v067Bp2303d*dc*dsc*dp*ic*isc*ip* depends: usbserial,usbcore intree: Y vermagic: 3.2.57 SMP mod_unload modversions 686 parm: debug:Debug enabled or not (bool)
可以看到pl2303又依赖于usbserial和usbcore.
下载linux内核源码（可以参考我的博文《debian下配置dynamic printk以及重新编译内核》），解压缩后进入该文件夹。
$ grep ‘pl2303‘ drivers/usb/serial/Makefile obj-$(CONFIG_USB_SERIAL_PL2303) += pl2303.o
$ grep ‘usbserial‘ drivers/usb/serial/Makefile
obj-$(CONFIG_USB_SERIAL) += usbserial.o
usbserial-y := usb-serial.o generic.o bus.o
usbserial-$(CONFIG_USB_SERIAL_CONSOLE) += console.o
usbserial-$(CONFIG_USB_EZUSB) += ezusb.o
$ grep ‘usbcore‘ drivers/usb/core/Makefile
usbcore-y := usb.o hub.o hcd.o urb.o message.o driver.o
usbcore-y += config.o file.o buffer.o sysfs.o endpoint.o
usbcore-y += devio.o notify.o generic.o quirks.o devices.o
usbcore-$(CONFIG_PCI) += hcd-pci.o
usbcore-$(CONFIG_USB_DEVICEFS) += inode.o
obj-$(CONFIG_USB) += usbcore.o
从搜索结果可以看出:
pl2303驱动由drivers/usb/serial/pl2303.c文件来生成的。
usbserial驱动是由drivers/usb/serial下的usb-serial.c generic.c bus.c这三个文件来生成的。
usbcore是由drivers/usb/core/下面的usb.c hub.c hcd.c urb.c message.c driver.c config.c file.c buffer.c sysfs.c endpoint.c
devio.c notify.c generic.c quirks.c devices.c hcd-pci.c inode.c这些文件生成的。
切换到root用户：
su
挂载debugfs:
# mount -t debugfs none /sys/kernel/debug/
对上面提到的所有文件使能"Dynamic debugging"：
root@debian:~# echo ‘file drivers/usb/serial/pl2303.c +p‘ > /sys/kernel/debug/dynamic_debug/control root@debian:~# echo ‘file drivers/usb/serial/usb-serial.c +p‘ > /sys/kernel/debug/dynamic_debug/control root@debian:~# echo ‘file drivers/usb/serial/generic.c +p‘ > /sys/kernel/debug/dynamic_debug/control root@debian:~# echo ‘file drivers/usb/serial/bus.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/usb.c +p‘ > /sys/kernel/debug/dynamic_debug/control^C
root@debian:~# echo ‘file drivers/usb/core/hub.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/hcd.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/urb.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/message.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/driver.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/config.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/file.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/buffer.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/sysfs.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/endpoint.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/device.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/notify.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/generic.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/quirks.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/devices.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/hci-pci.c +p‘ > /sys/kernel/debug/dynamic_debug/control
root@debian:~# echo ‘file drivers/usb/core/inode.c +p‘ > /sys/kernel/debug/dynamic_debug/control
先拔掉usb转串口线，然后删除pl2303驱动（因为之前已经插入过usb转串口，pl2303已经加载）：
sudo rmmod pl2303
再插入usb转串口线，在另一个控制台下执行命令：
$ dmesg | tail -n 35 [ 3405.314567] hub 1-0:1.0: state 7 ports 8 chg 0000 evt 0100 [ 3405.314587] hub 1-0:1.0: port 8, status 0501, change 0001, 480 Mb/s [ 3405.472015] hub 1-0:1.0: debounce: port 8: total 125ms stable 100ms status 0x501 [ 3405.528178] hub 1-0:1.0: port 8 not reset yet, waiting 50ms [ 3405.528197] usb usb5: usb wakeup-resume [ 3405.528203] usb usb5: usb auto-resume [ 3405.568011] hub 5-0:1.0: hub_resume [ 3405.568027] hub 5-0:1.0: port 2: status 0101 change 0001 [ 3405.584034] hub 1-0:1.0: state 7 ports 8 chg 0000 evt 0100 [ 3405.672026] hub 5-0:1.0: state 7 ports 2 chg 0004 evt 0000 [ 3405.672041] hub 5-0:1.0: port 2, status 0101, change 0000, 12 Mb/s [ 3405.784018] usb 5-2: new full-speed USB device number 4 using uhci_hcd [ 3405.936037] usb 5-2: default language 0x0409 [ 3405.946039] usb 5-2: udev 4, busnum 5, minor = 515 [ 3405.946044] usb 5-2: New USB device found, idVendor=067b, idProduct=2303 [ 3405.946049] usb 5-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0 [ 3405.946053] usb 5-2: Product: USB-Serial Controller [ 3405.946057] usb 5-2: Manufacturer: Prolific Technology Inc. [ 3405.946151] bus: ‘usb‘: add device 5-2 [ 3405.946228] usb 5-2: usb_probe_device [ 3405.946234] usb 5-2: configuration #1 chosen from 1 choice [ 3405.949040] usb 5-2: adding 5-2:1.0 (config #1, interface 0) [ 3405.949061] bus: ‘usb‘: add device 5-2:1.0 [ 3405.949110] usbserial_generic 5-2:1.0: usb_probe_interface [ 3405.949115] usbserial_generic 5-2:1.0: usb_probe_interface - got id [ 3406.014058] bus: ‘usb-serial‘: add driver pl2303 [ 3406.014092] USB Serial support registered for pl2303 [ 3406.014096] bus: ‘usb‘: add driver pl2303 [ 3406.027529] pl2303 5-2:1.0: usb_probe_interface [ 3406.027533] pl2303 5-2:1.0: usb_probe_interface - got id [ 3406.027539] pl2303 5-2:1.0: pl2303 converter detected [ 3406.039051] bus: ‘usb-serial‘: add device ttyUSB0 [ 3406.039201] usb 5-2: pl2303 converter now attached to ttyUSB0 [ 3406.039221] usbcore: registered new interface driver pl2303 [ 3406.039223] pl2303: Prolific PL2303 USB to serial adaptor driver
明显多了很多调试信息，更便于跟踪实际代码的执行情况。
下面分析插入usb转串口线时的执行情况.
考虑“[ 3405.314567] hub 1-0:1.0: state 7 ports 8 chg 0000 evt 0100”这一行输出信息。
我们只考虑driver/usb下执行的代码，所以只在该文件夹下搜索源代码。
$ grep -rnHi ‘chg.*evt‘ drivers/usb/ drivers/usb/core/hub.c:3586: dev_dbg(hub_dev, "state %d ports %d chg %04x evt %04x\n",
这一行代码位于hub_events函数，该函数被hub_thread调用：
static int hub_thread(void *__unused) { /* khubd needs to be freezable to avoid intefering with USB-PERSIST * port handover. Otherwise it might see that a full-speed device * was gone before the EHCI controller had handed its port over to * the companion full-speed controller. */ set_freezable(); do { hub_events(); wait_event_freezable(khubd_wait, !list_empty(&hub_event_list) || kthread_should_stop()); } while (!kthread_should_stop() || !list_empty(&hub_event_list)); pr_debug("%s: khubd exiting\n", usbcore_name); return 0; }
hub_thread是在usb_hub_init中创建的一个内核线程khubd的执行函数,这个内核线程开机后就会一直处于运行状态。
考虑“[ 3405.314587] hub 1-0:1.0: port 8, status 0501, change 0001, 480 Mb/s”这一行输出信息：
$ grep -rnHi ‘port.*status.*change.*\\n‘ drivers/usb/ drivers/usb/core/hub.c:859: "port %d: status %04x change %04x\n", drivers/usb/core/hub.c:3329: "port %d, status %04x, change %04x, %s\n", drivers/usb/gadget/dummy_hcd.c:1753: dev_dbg(dummy_dev(dum_hcd), "port status 0x%08x has changes\n", drivers/usb/host/xhci-ring.c:1565: xhci_dbg(xhci, "Port Status Change Event for port %d\n", port_id);
可以看出只有第两行输出信息可能和当前的输出有关系，此行代码位于hub_port_connect_change函数，
而hub_port_connect_change被hub_events函数调用。
考虑下一行输出“[ 3405.472015] hub 1-0:1.0: debounce: port 8: total 125ms stable 100ms status 0x501”。
$ grep -rnHi ‘debounce:‘ drivers/usb/ drivers/usb/core/hub.c:2898: "debounce: port %d: total %dms stable %dms status 0x%x\n",
该行输出信息位于hub_port_debounce函数，hub_port_debounce函数又被hub_port_connect_change所调用。
考虑下一行输出“[ 3405.528178] hub 1-0:1.0: port 8 not reset yet, waiting 50ms”。
$ grep -rnHi ‘reset yet,‘ drivers/usb/ drivers/usb/core/hub.c:2203: "port %d not %sreset yet, waiting %dms\n",
这行代码位于hub_port_wait_reset函数，hub_port_wait_reset又被hub_port_reset函数调用,hub_port_reset又被hub_port_init调用,
hub_port_init又被hub_port_connect_change函数调用。
下一行输出“[ 3405.528197] usb usb5: usb wakeup-resume”。
$ grep -rnHi ‘%sresume‘ drivers/usb/core drivers/usb/core/hcd.c:2012: dev_dbg(&rhdev->dev, "usb %sresume\n", drivers/usb/core/hub.c:2686: dev_dbg(&udev->dev, "usb %sresume\n", drivers/usb/core/hub.c:2737: dev_dbg(&udev->dev, "usb %sresume\n", "wakeup-");
查看代码后得知，与之匹配的是hub.c中2737行代码，位于usb_remote_wakeup中.
usb_remote_wakeup在好几个地方被调用，不清楚是哪个函数调用引起的。
下一行输出信息是：[ 3405.528203] usb usb5: usb auto-resume
根据上面的查新结果,很可能是被usb_port_resume或者hcd_bus_resume函数调用，而这两个函数都是被generic_resume函数所调用。
下一行输出信息：[ 3405.568011] hub 5-0:1.0: hub_resume
没有用grep搜索到有用信息，但是很可能是执行hub_resume函数输出的，查看hub_resume定义：
static int hub_resume(struct usb_interface *intf) { struct usb_hub *hub = usb_get_intfdata(intf); dev_dbg(&intf->dev, "%s\n", __func__); hub_activate(hub, HUB_RESUME); return 0; }
果然代码中有__func__，就是hub_resume。hub_resume没有被直接调用，它在hub_driver.resume=hub_resume中被定义。
下一行输出信息是:[ 3405.568027] hub 5-0:1.0: port 2: status 0101 change 0001
$ grep -rnHi ‘port.*status.*change.*\\n‘ drivers/usb/ drivers/usb/core/hub.c:859: "port %d: status %04x change %04x\n", drivers/usb/core/hub.c:3329: "port %d, status %04x, change %04x, %s\n", drivers/usb/gadget/dummy_hcd.c:1753: dev_dbg(dummy_dev(dum_hcd), "port status 0x%08x has changes\n", drivers/usb/host/xhci-ring.c:1565: xhci_dbg(xhci, "Port Status Change Event for port %d\n", port_id);
第一行搜索到的信息格式和输出信息相匹配。此行代码位于hub_activate中。而上一行中hub_resume恰好调用了hub_activate函数。
接下来三行输出信息：
[ 3405.584034] hub 1-0:1.0: state 7 ports 8 chg 0000 evt 0100 [ 3405.672026] hub 5-0:1.0: state 7 ports 2 chg 0004 evt 0000 [ 3405.672041] hub 5-0:1.0: port 2, status 0101, change 0000, 12 Mb/s
这三行信息和最前面的两行输出信息类似，不再重复分析了。 但是这里又重新从hub_event的开头部分开始执行程序。
下一行输出信息：[ 3405.784018] usb 5-2: new full-speed USB device number 4 using uhci_hcd
$ grep -rnHi ‘USB device number‘ drivers/usb/ drivers/usb/core/hub.c:3035: "%s %s USB device number %d using %s\n", drivers/usb/core/hub.c:3149: "%s SuperSpeed USB device number %d using %s\n",
第一行搜索到内容与输出信息完全匹配，该代码位于hub_port_init中。hub_port_init又被hub_port_connect_change调用。
下一行输出信息：[ 3405.936037] usb 5-2: default language 0x0409
$ grep -rnHi ‘default language‘ drivers/usb/ drivers/usb/core/message.c:790: dev_dbg(&dev->dev, "default language 0x%04x\n",
该行代码位于usb_get_langid中,usb_get_langid又被usb_string函数调用。调用usb_string的函数不好分析，留待以后再看。
下一行输出信息：[ 3405.946039] usb 5-2: udev 4, busnum 5, minor = 515
$ grep -rnHi ‘udev.*busnum.*minor‘ drivers/usb/ drivers/usb/core/hub.c:1971: dev_dbg(&udev->dev, "udev %d, busnum %d, minor = %d\n",
该代码位于usb_new_device中，而usb_new_device又被usb_port_connect_change函数所调用。
而查看该行代码前，执行了usb_enumerate_device函数。该函数调用了usb_cache_string,而usb_cache_string又调用了usb_string.
所以上一行的输出信息就是在调用usb_enumerate_device时产生的。
接下来四行信息：
[ 3405.946044] usb 5-2: New USB device found, idVendor=067b, idProduct=2303 [ 3405.946049] usb 5-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0 [ 3405.946053] usb 5-2: Product: USB-Serial Controller [ 3405.946057] usb 5-2: Manufacturer: Prolific Technology Inc.
之前在我的博文《linux下无线鼠标驱动执行流程》中已经找到了执行这几行代码的函数，其名称是announce_device,该函数也被usb_new_device调用。
下一行输出信息：[ 3405.946151] bus: ‘usb‘: add device 5-2
这行输出信息在函数bus_add_device(drivers/base/bus.c)被执行。这是因为我在配置"dynamic debugging"时执行了下面的命令：
echo ‘file bus.c +p‘ > /sys/kernel/debug/dynamic_debug/control
后来看没有只是打开了drivers/base/bus.c，而不是打开drivers/usb/core/bus.c的"dynamic debugging"功能，所以才添加了路径名称来保证唯一性。
但是以前打开的drivers/base/bus.c中的"dynamic debugging"功能并没有关闭，所以这里有相关的信息显示。
bus_add_device在device_add函数中被调用,device_add又被usb_new_device调用。
下一行输出信息：[ 3405.946228] usb 5-2: usb_probe_device
猜想是执行usb_probe_device时显示的信息，查看usb_probe_device函数代码发现果然有下面一行代码：
dev_dbg(dev, "%s\n", __func__);
usb_probe_device可能是在device_add调用bus_probe_device时调用的(过程比较复杂，不再详述）。
下一行输出信息：[ 3405.946234] usb 5-2: configuration #1 chosen from 1 choice
$ grep -rnHi ‘chosen from‘ drivers/usb/ drivers/usb/core/generic.c:145: "configuration #%d chosen from %d choice%s\n", drivers/usb/core/generic.c:150: "no configuration chosen from %d choice%s\n",
只有第一行搜索信息与实际输出信息格式相匹配。
该行代码位于usb_choose_configuration函数中，usb_choose_configuration函数又被generic_probe函数调用。
代码中显示usb_generic_driver和usb_serial_generic_driver这两个驱动都使用了generic_probe函数执行probe功能。
此处应该使用的是usb_generic_driver的generic_probe函数。
下一行输出信息：[ 3405.949040] usb 5-2: adding 5-2:1.0 (config #1, interface 0)
$ grep -rnHi ‘adding.*config.*interface‘ drivers/usb/ drivers/usb/core/message.c:1861: "adding %s (config #%d, interface %d)\n",
该代码位于usb_set_configuration中,usb_set_configuration函数被generic_probe函数所调用。
下一行输出信息：[ 3405.949061] bus: ‘usb‘: add device 5-2:1.0
跟前面其中一行的情况相同，执行bus_add_device时调用了这个函数，bus_add_device又被device_add函数所调用。
下一行输出信息：[ 3405.949110] usbserial_generic 5-2:1.0: usb_probe_interface
$ grep -rnHi ‘usbserial_generic‘ drivers/usb/ drivers/usb/serial/generic.c:53: .name = "usbserial_generic",
看起来很像是执行usb_probe_interface时给出的输出信息，查看函数源码，果然有下一行代码：
dev_dbg(dev, "%s\n", __func__);
下一行输出信息：[ 3405.949115] usbserial_generic 5-2:1.0: usb_probe_interface - got id
在查看usb_probe_interface函数源码时看到有类似于"got id"之类的输出，所以是在usb_probe_interface中被调用。
下一行输出信息：[ 3406.014058] bus: ‘usb-serial‘: add driver pl2303
$ grep -rnHi ‘add driver‘ drivers/base drivers/base/bus.c:635: pr_debug("bus: ‘%s‘: add driver %s\n", bus->name, drv->name);
看输出信息中第一个冒号前是usb，再拿前面的例子作对比，可以知道应该是在drivers/base下执行代码产生类似的输出。
该代码位于bus_add_driver中，bus_add_driver又被driver_register函数所调用。
下一行输出信息：[ 3406.014092] USB Serial support registered for pl2303
$ grep -rnHi ‘registered for‘ drivers/usb drivers/usb/serial/usb-serial.c:1389: printk(KERN_INFO "USB Serial support registered for %s\n", drivers/usb/gadget/s3c-hsotg.c:3121: * registered for each available).
搜索到的第一行信息与输出信息格式一致。
该代码位于usb_serial_register中，usb_serial_register又被pl2303_init所调用。
下一行输出信息：[ 3406.039051] bus: ‘usb-serial‘: add device ttyUSB0
跟前面一些输出信息类似，也是被bus_add_device调用，bus_add_device又被device_add调用。
下一行输出信息：[ 3406.039201] usb 5-2: pl2303 converter now attached to ttyUSB0
$ grep -rnHi ‘attached to ttyUSB‘ drivers/usb drivers/usb/serial/bus.c:83: "%s converter now attached to ttyUSB%d\n",
此代码位于usb_serial_device_probe中。代码中还有这样的赋值：usb_serial_bus_type.probe=usb_serial_device_probe
下一行信息输出：[ 3406.039221] usbcore: registered new interface driver pl2303
$ grep -rnHi ‘registered new interface‘ drivers/usb drivers/usb/core/driver.c:888: pr_info("%s: registered new interface driver %s\n",
该代码位于usb_register_driver函数中。
文件include/linux/usb.h中有下面的定义：
#define usb_register(driver) usb_register_driver(driver, THIS_MODULE, KBUILD_MODNAME)
所以有可能是调用usb_register时输出了这行信息。 pl2303_init也调用了usb_register。
最后一行输出信息：[ 3406.039223] pl2303: Prolific PL2303 USB to serial adaptor driver
这行输出信息对应pl2303_init中的下列代码：
printk(KERN_INFO KBUILD_MODNAME ": " DRIVER_DESC "\n");
从上面的分析可以看出，执行程序时会运行drivers/base下的一些代码。
拔掉usb转串口线，然后使能drivers/base下所有文件的"dynamic debugging"功能：
echo ‘file drivers/base/* +p‘ > /sys/kernel/debug/dynamic_debug/control
再插入和移除usb转串口线，可以得到下面的信息：
[18177.932295] hub 1-0:1.0: state 7 ports 8 chg 0000 evt 0100 [18177.932311] hub 1-0:1.0: port 8, status 0501, change 0001, 480 Mb/s [18178.060035] hub 1-0:1.0: debounce: port 8: total 100ms stable 100ms status 0x501 [18178.116224] hub 1-0:1.0: port 8 not reset yet, waiting 50ms [18178.116237] usb usb5: usb wakeup-resume [18178.116242] usb usb5: usb auto-resume [18178.156009] hub 5-0:1.0: hub_resume [18178.156023] hub 5-0:1.0: port 2: status 0101 change 0001 [18178.172085] hub 1-0:1.0: state 7 ports 8 chg 0000 evt 0100 [18178.260062] hub 5-0:1.0: state 7 ports 2 chg 0004 evt 0000 [18178.260079] hub 5-0:1.0: port 2, status 0101, change 0000, 12 Mb/s [18178.372037] usb 5-2: new full-speed USB device number 11 using uhci_hcd [18178.525033] usb 5-2: default language 0x0409 [18178.535037] usb 5-2: udev 11, busnum 5, minor = 522 [18178.535041] usb 5-2: New USB device found, idVendor=067b, idProduct=2303 [18178.535043] usb 5-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0 [18178.535045] usb 5-2: Product: USB-Serial Controller [18178.535047] usb 5-2: Manufacturer: Prolific Technology Inc. [18178.535130] bus: ‘usb‘: add device 5-2 [18178.535182] usb 5-2: usb_probe_device [18178.535186] usb 5-2: configuration #1 chosen from 1 choice [18178.538030] usb 5-2: adding 5-2:1.0 (config #1, interface 0) [18178.538042] bus: ‘usb‘: add device 5-2:1.0 [18178.538071] usbserial_generic 5-2:1.0: usb_probe_interface [18178.538074] usbserial_generic 5-2:1.0: usb_probe_interface - got id [18178.538085] pl2303 5-2:1.0: usb_probe_interface [18178.538088] pl2303 5-2:1.0: usb_probe_interface - got id [18178.538092] pl2303 5-2:1.0: pl2303 converter detected [18178.550035] bus: ‘usb-serial‘: add device ttyUSB0 [18178.550140] usb 5-2: pl2303 converter now attached to ttyUSB0 [18383.168069] hub 5-0:1.0: state 7 ports 2 chg 0000 evt 0004 [18383.168095] hub 5-0:1.0: port 2, status 0100, change 0003, 12 Mb/s [18383.168101] usb 5-2: USB disconnect, device number 11 [18383.168105] usb 5-2: unregistering device [18383.168109] usb 5-2: unregistering interface 5-2:1.0 [18383.168209] bus: ‘usb‘: remove device 5-2:1.0 [18383.168238] bus: ‘usb-serial‘: remove device ttyUSB0 [18383.168351] pl2303 ttyUSB0: pl2303 converter now disconnected from ttyUSB0 [18383.168374] pl2303 5-2:1.0: device disconnected [18383.168402] usb 5-2: usb_disable_device nuking all URBs [18383.168746] bus: ‘usb‘: remove device 5-2 [18383.296029] hub 5-0:1.0: debounce: port 2: total 100ms stable 100ms status 0x100 [18386.008044] hub 5-0:1.0: hub_suspend [18386.008058] usb usb5: bus auto-suspend, wakeup 1
18177和18178开头部分是插入usb转串口时产生的信息。
而18383和18386开头部分是移除usb转串口时产生的信息。
仔细看了一下输出信息，似乎和之前的输出信息并没有什么差别，也不再仔细分析了，感兴趣的话可以自己分析看看。
debian下使用dynamic printk分析usb转串口驱动执行流程,布布扣,bubuko.com
debian下使用dynamic printk分析usb转串口驱动执行流程
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原文地址：http://www.cnblogs.com/qiaoqiao2003/p/3798976.html
