July 2011 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Regarding remap_pfn_page
by mindentropy July 21, 2011

July 21, 2011

Hi, When I mmap pages via remap_pfn_page method would the physical frames assigned the linear address be contiguous? If yes what would happen if I mmap a huge range? Thanks.

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PCI Driver not writing to Config Space
by Giriprasad Deviprasad July 20, 2011

July 20, 2011

Hi All, I have a pci driver like: define VENDOR_ID 0x1415 #define DEVICE_ID1 0xc140 #include<linux/module.h> #include<linux/version.h> #include<linux/kernel.h> #include<linux/pci.h> #include<linux/ioport.h> #include<asm/unistd.h> #include<linux/slab.h> #include<linux/fs.h> #include<asm/uaccess.h> #include<asm/io.h> #include<linux/kdev_t.h> #include<asm/fcntl.h> #include<linux/sched.h> #include<linux/wait.h> #include<linux/errno.h> #include<asm/irq.h> #include<asm/ioctl.h> #include<linux/string.h> #include<linux/interrupt.h> init_module (void) { short int curr_device; dev = pci_find_device (VENDOR_ID, DEVICE_ID1, NULL); j = pci_enable_device (dev); curr_device = 0; printk("Init : Reading and writing Config space.........\n"); pci_read_config_word (dev, 0x02, (u16 *)&curr_device); printk("Init : Current Device id = %x\n", (curr_device & 0x00FFFF)); curr_device = 0xc145; pci_write_config_word (dev, 0x02, curr_device); pci_read_config_word (dev, 0x02, (u16 *)&curr_device); printk("Init : After writing to Config space, Current Device id = %x\n", (curr_device & 0x00FFFF)); return 0; } void cleanup_module (void) { printk ("Closing pci \n"); } When I insmod this driver after build, it shows: Jul 20 15:11:03 localhost kernel: Init : Reading and writing Config space......... Jul 20 15:11:03 localhost kernel: Init : Current Device id = c140 Jul 20 15:11:03 localhost kernel: Init : After writing to Config space, Current Device id = c140 Any clues as to why is not writing 0xc145 to the pci config space? curr_device = 0xc145; pci_write_config_word (dev, 0x02, curr_device); Thanks & Regards, D.Giriprasad

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why backtiks for a word?
by zeal July 19, 2011

July 19, 2011

Hi list, We often see that `a word what you like'. But i get confused on it. Why is it `word' but not 'word' or what else? -- Cheers - zeal

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Need help understanding memory models, cpu modes and address translation
by Vaibhav Jain July 17, 2011

July 17, 2011

Hi, I am eager to understand the basics of Memory models (flat, segmented etc) , CPU modes (real,protected) and address translation (physical to logical etc.) and how all of them work together. I am very confused about this and would really appreciate if someone could provide good references to these topics. Thanks Vaibhav Jain

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interview question how does application connects to device
by Bond July 17, 2011

July 17, 2011

This is an interview question. I had written device driver for a char device so I know that code structure looks like this struct file_operations something { .owner=my_device_open; .read=my_device_read; .close=my_device_close; .write=my_device_write; } When the device driver is active then in /dev/mydevice you can actually read and write into it. But what I was not clear is how an application will read or write to this device. I know insmod will insert the module to kernel,and register_chrdev(); will register the driver in kernel but how will application program communicate with this driver. My answer was In unix it simply opens the device node as a file and sends/receives data and commands from it. But he was expecting some thing more complex.

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LinuxCon Japan Videos
by Paul Fisher July 16, 2011

July 16, 2011

Can anybody point me at this year's LinuxCon Japan video recordings? Are they available somewhere? I'm aware of the Linus interview, I am intrested in talks and panels. --paul

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Difference between Processors
by Niamathullah sharief July 16, 2011

July 16, 2011

Dear friends, Can anyone tell me what is the exact difference between CISC and RISC processors? Which one is best and how it varies? Please tell me. Thank you

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linux dma apis
by Abhishek Batta July 16, 2011

July 16, 2011

Hello everyone, Please point me to some useful links to start understanding linux dma . Thanks

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change kthread priority
by loody July 15, 2011

July 15, 2011

Dear all: I have some questions about kthread: 1. can we change kthread priority through user mode program? 2. I found some functions that may be helpful. sched_getscheduler sched_setscheduler When I use them in user mode, the return value of sched_setscheduler is fail. there is a thread talking about this, http://www.spinics.net/lists/linux-rt-users/msg06588.html What makes me confuse is "these 2 functions is used in user mode or kernel mode?" -- Regards, -- Regards, -- Regards,

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Questions regarding console drivers..
by sandeep kumar July 15, 2011

July 15, 2011

Hi all, I have gone through the kernel/kernel/printk.c file. And i have the following questions.. I have some rough idea of several things, but i need to conform them 1) What is a console driver? --> My idea is it allows the kernel to input or output the characters to or from a particular device. 2) Why so many command-line consoles are needed? --> (if first qn is right...why cant u use single console to several devices) 3) What is a boot console & real console? 4) How to know how many number of consoles are running at a time? 5) In the boot command line we will pass one console name "console=ttyXXX", other than that where the remaining consoles are being registered? Please answer these questions so that i can have furthur understanding Thank you all.. -- With regards, Sandeep Kumar Anantapalli,

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