talk.mgp

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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page
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%size 20, font "knife"
Write a real
Linux driver
%font "standard"
%size 6
Greg Kroah-Hartman
%size 5
SuSE Labs / Novell
%size 4
%font "email"
http://www.kroah.com/usb.tar.gz

gregkh@suse.de
greg@kroah.com
%font "standard"
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Agenda


	Intro to kernel modules

	sysfs basics

	USB basics

	Driver to device binding

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Agenda - continued


	Using sysfs

	Sending and receiving USB data
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Hello world kernel module

%font "typewriter", size 3.3
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/module.h>

 static int __init gotemp_init(void)
 {
         printk(KERN_INFO "Hello from the kernel!\\n");
         return 0;
 }

 static void __exit gotemp_exit(void)
 {
 }

 module_init(gotemp_init);
 module_exit(gotemp_exit);

 MODULE_AUTHOR("My name here");
 MODULE_DESCRIPTION("Simple driver");
 MODULE_LICENSE("GPL");
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Makefile



%font "typewriter", size 4
obj-m := hello.o

KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD       := $(shell pwd)

all:
        $(MAKE) -C $(KERNELDIR) M=$(PWD)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Manipulating Modules

	See the module informaion
%font "typewriter", size 5
        modinfo hello.ko
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	Insert the module into the kernel
%font "typewriter", size 5
        insmod hello.ko
%font "standard"

	See that it did something
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        lsmod
        dmesg
%font "standard"

	Remove the module from the kernel
%font "typewriter", size 5
        rmmod hello
%font "standard"

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

sysfs crash course


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"Web woven by a spider on drugs"
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%right
- lwn.net       


        
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/proc
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 is for processes, not for drivers

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

USB crash course


	devices and configs and interfaces oh my

	How do you identify a unique device?
       
%cont, font "typewriter", size 5
MODULE_DEVICE_TABLE
%font "standard"
		"it just works"


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Bind to the device - step 1



%font "typewriter", size 4
\#define VENDOR_ID   0x08f7
\#define PRODUCT_ID  0x0002

/* table of devices that work with this driver */
static struct usb_device_id id_table [] = {
        { USB_DEVICE(VENDOR_ID, PRODUCT_ID) },
        { },
};
MODULE_DEVICE_TABLE(usb, id_table);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Bind to the device - step 2


%font "typewriter", size 3.5
static int gotemp_probe(struct usb_interface *interface, 
                        const struct usb_device_id *id)
{
        dev_info(&interface->dev,
                 "USB GoTemp device now attached\\n");
        return 0;
}

static void gotemp_disconnect(struct usb_interface *interface)
{
        dev_info(&interface->dev,
                 "USB GoTemp now disconnected\\n");
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Bind to the device - step 3


%font "typewriter", size 4
static struct usb_driver gotemp_driver = {
        .name =       "gotemp",
        .probe =      gotemp_probe,
        .disconnect = gotemp_disconnect,
        .id_table =   id_table,
};

static int __init gotemp_init(void)
{
        return usb_register(&gotemp_driver);
}

static void __exit gotemp_exit(void)
{
        usb_deregister(&gotemp_driver);
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Device specific structure



%font "typewriter", size 5
struct gotemp {
        struct usb_device *udev;
        int temperature;
};

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Device specific structure

%font "typewriter", size 3
static int gotemp_probe(struct usb_interface *interface,
                        const struct usb_device_id *id)
{
        struct usb_device *udev = interface_to_usbdev(interface);
        struct gotemp *gdev;

        gdev = kmalloc(sizeof(struct gotemp), GFP_KERNEL);
        if (gdev == NULL) {
                dev_err(&interface->dev, "Out of memory\\n");
                return -ENOMEM;
        }
        memset(gdev, 0x00, sizeof(*gdev));

        gdev->udev = usb_get_dev(udev);

        usb_set_intfdata(interface, gdev);

        dev_info(&interface->dev, "USB GoTemp device now attached\\n");
        return 0;
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Device specific structure

%font "typewriter", size 3
static void gotemp_disconnect(struct usb_interface *interface)
{
        struct gotemp *gdev;

        gdev = usb_get_intfdata(interface);
        usb_set_intfdata(interface, NULL);

        usb_put_dev(gdev->udev);

        kfree(gdev);

        dev_info(&interface->dev, "USB GoTemp now disconnected\\n");
}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Make a sysfs file

%font "typewriter", size 3.5
static ssize_t show_temperature(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        struct usb_interface *intf = to_usb_interface(dev);
        struct gotemp *gdev = usb_get_intfdata(intf);

        return sprintf(buf, "%d\\n", gdev->temperature);
}
static DEVICE_ATTR(temperature, S_IRUGO, show_temperature, NULL);
%font "standard"

	In 
%cont, font "typewriter", size 4
gotemp_probe:
%font "typewriter", size 3.5
        device_create_file(&interface->dev, &dev_attr_temperature);

%font "standard"
	In 
%cont, font "typewriter", size 4
gotemp_disconnect:
%font "typewriter", size 3.5
        device_remove_file(&interface->dev, &dev_attr_temperature);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Simple USB data transfer

%font "typewriter", size 3
\#define CMD_ID_START_MEASUREMENTS 0x18
\#define CMD_ID_INIT               0x1A

struct output_packet {
        u8 cmd;
        u8 params[7];
} __attribute__((packed));

static int send_cmd(struct gotemp *gdev, u8 cmd)
{
        struct output_packet *pkt;
        int retval;

        pkt = kzalloc(sizeof(*pkt), GFP_KERNEL);
        if (!pkt)
                return -ENOMEM;
        pkt->cmd = cmd;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Simple USB data transfer

%font "typewriter", size 3
%fore "red"
send_cmd() continued:
%fore "black"
        retval = usb_control_msg(gdev->udev,
                                 usb_sndctrlpipe(gdev->udev, 0),
                                 0x09,    /* bRequest = SET_REPORT */
                                 0x21,    /* bRequestType = 00100001 */
                                 0x0200,  /* or is it 0x0002? */
                                 0x0000,  /* interface 0 */
                                 pkt, sizeof(*pkt), 10000);
        if (retval == sizeof(*pkt))
                retval = 0;
        kfree(pkt);
        return retval;
}

static void init_dev(struct gotemp *gdev)
{
        /* First send an init message */
        send_cmd(gdev, CMD_ID_INIT);

        /* Start sending measurements */
        send_cmd(gdev, CMD_ID_START_MEASUREMENTS);
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

"Real" USB data transfers

%font "typewriter", size 7, center
struct urb;
%font "standard", leftfill

	dynamically created

	fire and forget

	high data rates

	Like network skb packets
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

urb in the device structure




%font "typewriter", size 4
struct gotemp {
        struct usb_device *udev;
        int temperature;
        unsigned char *int_in_buffer;
        struct urb *int_in_urb;
};

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Find the endpoint



%font "typewriter", size 3
%fore "red"
gotemp_probe():
%fore "black"

        /* find the one control endpoint of this device */
        endpoint = &interface->cur_altsetting->endpoint[0].desc;

        buffer_size = le16_to_cpu(endpoint->wMaxPacketSize);

        gdev->int_in_buffer = kmalloc(buffer_size, GFP_KERNEL);
        if (!gdev->int_in_buffer) {
                dev_err(&interface->dev,
                        "Could not allocate buffer\\n");
                goto error;
        }

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Create the urb



%font "typewriter", size 3
%fore "red"
gotemp_probe():
%fore "black"

        gdev->int_in_urb = usb_alloc_urb(0, GFP_KERNEL);
        if (!gdev->int_in_urb) {
                dev_err(&interface->dev, "No free urbs available\\n");
                goto error;
        }
        usb_fill_int_urb(gdev->int_in_urb, udev,
                         usb_rcvintpipe(udev,
                                        endpoint->bEndpointAddress),
                         gdev->int_in_buffer, buffer_size,
                         read_int_callback, gdev,
                         endpoint->bInterval);


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

Submit the urb



%font "typewriter", size 3
%fore "red"
init_dev():
%fore "black"

        /* kick off interrupt urb */
        retval = usb_submit_urb(gdev->int_in_urb, GFP_KERNEL);
        if (retval)
                dev_err(&gdev->udev->dev,
                        "Error %d submitting interrupt urb\\n",
                        retval);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

The data from the device


%font "typewriter", size 4

struct measurement_packet {
        u8    measurements_in_packet;
        u8    rolling_counter;
        le16  measurement0;
        le16  measurement1;
        le16  measurement2;
} __attribute__((packed));


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

The urb callback


%font "typewriter", size 3
static void read_int_callback(struct urb *urb, struct pt_regs *regs)
{
        struct gotemp *gdev = urb->context;
        struct measurement_packet *measurement = urb->transfer_buffer;
        int retval;

        switch (urb->status) {
        case 0: break;
        case -ECONNRESET:
        case -ENOENT:
        case -ESHUTDOWN:
                /* this urb is terminated, clean up */
                dbg("urb shutting down with status: %d",
                    urb->status);
                return;
        default:
                dbg("nonzero urb status received: %d",
                    __FUNCTION__, urb->status);
                goto exit;
        }

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page

The urb callback


%font "typewriter", size 3
%fore "red"
read_int_callback() continued:
%fore "black"

        gdev->temperature = le16_to_cpu(measurement->measurement0);

exit:
        retval = usb_submit_urb(urb, GFP_ATOMIC);
        if (retval)
                dev_err(&urb->dev->dev,
                        "Error %d submitting interrupt urb\\n",
                        retval);
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%page
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The End
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