linux driver overview

8/9/2019 Linux Driver Overview

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Linux Driver OverviewLinux Driver Overview

::

http://www.ntut.edu.tw/~s4599001http://www.ntut.edu.tw/~s4599001


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Operating System LinuxOperating System Linux Operating systemOperating system

Kernel space/User spaceKernel space/User space MMUMMU mutex/semaphore/interruptmutex/semaphore/interrupt

Task structureTask structure ptrace/mmu/signal/task relation /process idptrace/mmu/signal/task relation /process id file/timer/semaphores/miscfile/timer/semaphores/misc

Main algorithmMain algorithm Signal handingSignal handing InterruptInterrupt

TaskletsTasklets Bottom havesBottom haves

Software interruptSoftware interruptmax 32max 32 Void open_sorftirq(int nr, void (*action) (structure softirq_action *, void *data)Void open_sorftirq(int nr, void (*action) (structure softirq_action *, void *data) Raise_softirq()Raise_softirq()

SchedulerScheduler SCHED_FIFO/SCHED_RR/SCHED_OTHERSCHED_FIFO/SCHED_RR/SCHED_OTHER


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MutexMutex

DefinitionDefinition In computer programming, a mutex is aIn computer programming, a mutex is a

program object that allows multiple programprogram object that allows multiple programthreads to share the same resource, such asthreads to share the same resource, such asfile access, but not simultaneously.file access, but not simultaneously.

Andrea Steinbach and Angelika Schofer,Andrea Steinbach and Angelika Schofer,as a master's thesis at Rheinischeas a master's thesis at RheinischeFriedrichFriedrich--Wilhelms University.Wilhelms University.


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SemaphoreSemaphore

DefinitionDefinition A semaphore is a protected variable (or abstract dataA semaphore is a protected variable (or abstract data

type) and constitutes the classic method fortype) and constitutes the classic method forrestricting access to shared resources (e.g. storage)restricting access to shared resources (e.g. storage)in a multiprogramming environment.in a multiprogramming environment.

SampleSample Dining philosophers problemDining philosophers problem

do not prevent all deadlocksdo not prevent all deadlocks

invented by Edsger Dijkstra and first used in theinvented by Edsger Dijkstra and first used in theTHE operating systemTHE operating system


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Semaphore ProgrammingSemaphore Programming

P(Semaphore s)P(Semaphore s){{

await s > 0 then s = sawait s > 0 then s = s--1; /* must be atomic once s > 0 is detected */1; /* must be atomic once s > 0 is detected */}}

V(Semaphore s)V(Semaphore s){{

s = s+1; /* must be atomic */s = s+1; /* must be atomic */}}Init(Semaphore s, Integer v)Init(Semaphore s, Integer v){{

s = v;s = v;}}


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Driver implementation in LinuxDriver implementation in Linux

Driver specificationsDriver specifications Char driversChar drivers

ConsoleConsole Serial portSerial port

Block driversBlock drivers

DMA transferDMA transfer

Network interfacesNetwork interfaces

IO port / IO memoryIO port / IO memory


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Driver implementation in LinuxDriver implementation in Linux

InterruptInterrupt int request_irq(unsigned int irq,voidint request_irq(unsigned int irq,void

(*handler)(int, void *, struct pt_regs(*handler)(int, void *, struct pt_regs*),unsigned long flags,const char*),unsigned long flags,const char*dev_name,void *dev_id);*dev_name,void *dev_id);

void free_irq(unsigned int irq, void *dev_id);void free_irq(unsigned int irq, void *dev_id);


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Writing Linux Device DriverWriting Linux Device Driver

Header filesHeader files

#include #include

#include #include

#include #include

#include #include

#include #include

#include #include

#include #include


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Initialize register (clear)Initialize register (clear)static int test_open(struct inode *inodePtr, struct file *fp)static int test_open(struct inode *inodePtr, struct file *fp)

{{

printk( "Enter open routine.printk( "Enter open routine.\\n" );n" );

return 0;return 0;}}

static int test_release(struct inode *inodePtr, struct file *fp)static int test_release(struct inode *inodePtr, struct file *fp)

{{

MOD_DEC_USE_COUNT;MOD_DEC_USE_COUNT;printk( "Enter test_releaseprintk( "Enter test_release\\n" );n" );

return 0;return 0;

}}


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OperationOperationstatic ssize_t test_read(struct file *fp, char *buf, size_t len, loff_tstatic ssize_t test_read(struct file *fp, char *buf, size_t len, loff_t

*offset)*offset){{

printk( "Enter test_readprintk( "Enter test_read\\n" );n" );return len;return len;

}}

static ssize_t test_write(struct file *fp, char *buf, size_t len, loff_tstatic ssize_t test_write(struct file *fp, char *buf, size_t len, loff_t*offset)*offset)

{{ printk( "Enter test_writeprintk( "Enter test_write\\n" );n" );return len;return len;

}}


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Writing Linux Device DriverWriting Linux Device DriverMappingMapping

structstructfile_operationsfile_operations test_fops =test_fops =

{{

read:read: test_read,test_read,

write:write: test_write,test_write,

open:open: test_open,test_open,

release:release: test_release,test_release,ioctl:ioctl: test_ioctl,test_ioctl,

};};


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static int test_ioctl(struct inode *inodePtr, structstatic int test_ioctl(struct inode *inodePtr, structfile *fp, unsignedfile *fp, unsigned int cmd, unsigned long argint cmd, unsigned long arg))

{{switch( cmd ){switch( cmd ){

default:default:break;break;

}}return 0;return 0;

}}


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Entry point V.S. Exit pointEntry point V.S. Exit pointintinttest_init_moduletest_init_module(void)(void){{

register_chrdevregister_chrdev(( 100100, testName, &test_fops );, testName, &test_fops );

printk( "Init test moduleprintk( "Init test module\\n" );n" );

return 0;return 0;}}

voidvoid test_cleanup_moduletest_cleanup_module(void)(void){{

unregister_chrdevunregister_chrdev(( 100100, testName );, testName );

printk( "UnInit testprintk( "UnInit test\\n" );n" );

}}

module_initmodule_init( test_init_module );( test_init_module );module_exitmodule_exit( test_cleanup_module );( test_cleanup_module );

Entry point

Exit point


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Create EnvironmentCreate Environment

CompilerCompiler gccgcc --D__KERNEL__D__KERNEL__ --DMODULEDMODULE --I/usr/src/linuxI/usr/src/linux--2.4.22/include2.4.22/include --cc --OO --Wall drv.cWall drv.c --o drv.oo drv.o

Make nodeMake node

mknod /dev/test cmknod /dev/test c 100100 00

Check nodeCheck nodecrwcrw--rwrw--rwrw-- 1 root dialout 4, 64 Jun 30 11:19 test1 root dialout 4, 64 Jun 30 11:19 test

crwcrw--rwrw--rwrw-- 1 root dialout 4, 65 Aug 16 00:00 ttyS11 root dialout 4, 65 Aug 16 00:00 ttyS1


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Writing ApplicationWriting Application

int main(int argc, char *argv[])int main(int argc, char *argv[]){{

int fd;int fd;char buf[256] = "Hello World!!";char buf[256] = "Hello World!!";

fd = open(fd = open( "/dev/test"/dev/test, O_RDWR );, O_RDWR );if ( fd ==if ( fd == --1 )1 ){{

printf( "Open drv driver fail.[Application]printf( "Open drv driver fail.[Application]\\nn ););returnreturn --1;1;

}}write( fd, buf, 6 );write( fd, buf, 6 );close( fd );close( fd );return 0;return 0;

}}


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Implementation in Embedded LinuxImplementation in Embedded Linux

NOMMU (arm as example)NOMMU (arm as example) Uclinux(ww.uclinux.org)Uclinux(ww.uclinux.org)

MMUMMU http://www.arm.linux.org.uk/http://www.arm.linux.org.uk/

Other versionOther version http://www.linux.org/http://www.linux.org/


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Implementation in Embedded LinuxImplementation in Embedded Linux

The driver in embedded linuxThe driver in embedded linux Most implement in setting registersMost implement in setting registers

The different in mmu/nommuThe different in mmu/nommu mmummu

The same except less supportThe same except less support

nommunommu Almost no difference about address in user space /kernelAlmost no difference about address in user space /kernel

sapcesapce


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Recommended Books && web sitesRecommended Books && web sites

Linux Document ProjectLinux Document Project http://www.tldp.orghttp://www.tldp.org

AdvacendAdvacend linuxlinux programmingprogramming http://www.advancedlinuxprogramming.com/alphttp://www.advancedlinuxprogramming.com/alp--folderfolder

Linux device driversLinux device drivers http://www.xml.com/ldd/chapter/book/http://www.xml.com/ldd/chapter/book/

LINUXLINUX

Linux kernel programming M BeckLinux kernel programming M Beck Understanding the LINUX KERNELUnderstanding the LINUX KERNEL BovetBovet && CesatiCesati

Linux server hacksLinux server hacks OthersOthersIn the diskIn the disk


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Introduce to source navigatorIntroduce to source navigator

http://sourcenav.sourceforge.net/http://sourcenav.sourceforge.net/


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Q&A


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Define in Define in

struct file_operations {struct file_operations {

struct module *owner;struct module *owner;

ssize_t (*read) (struct file *, char *, size_t, loff_t *);ssize_t (*read) (struct file *, char *, size_t, loff_t *);

ssize_t (*write) (struct file *, const char *, size_t, loff_t *);ssize_t (*write) (struct file *, const char *, size_t, loff_t *);

int (*ioctl) (struct inode *, struct file *, unsigned int,int (*ioctl) (struct inode *, struct file *, unsigned int,unsigned long);unsigned long);

int (*open) (struct inode *, struct file *);int (*open) (struct inode *, struct file *);

int (*release) (struct inode *, struct file *);int (*release) (struct inode *, struct file *);};};

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