March 2018 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Update required packages to compile Linux Kernel
by Jefferson Capovilla May 5, 2018

May 5, 2018

Hi, I followed the tutorial available in this link: https://kernelnewbies.org/OutreachyfirstpatchSetup and noticed that it's necessary to install three more packages during step "Install some packages". The missing packages are: *bison flex libelf-dev* Could someone please update this info there? -- -- Thanks, Jeff

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V4l2 Sensor driver and V4l2 ctrls
by MUHAMMED ASAD P T April 3, 2018

April 3, 2018

Hi All, In reference sensor drivers, they used the V4L2_CID_DV_RX_POWER_PRESENT v4l2 ctrl. It is a standard ctrl and created using v4l2_ctrl_new_std(). The doubts are: 1. Whether in our sensor driver, we need to create this Control Id or not. How to take the decision on this. Since this is the standard ctrl. When we need to use these standard ctrls?? 2. In Sensor driver, the ctrls creation is anything depends on the bridge driver. Based on bridge driver, whether we need to create any ctrls in Sensor driver. This question belongs to design of the sensor driver. Thanks & Regards - Asad IQ Root Technologies

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Set SO_TCP_NODELAY (disabling the Nagle Algorithm)
by Naruto Nguyen April 1, 2018

April 1, 2018

Hello everyone, As I know we have a socket option SO_TCP_NODELAY to disable Nagle Algorithm, and I found it is implemented in TCP/IP stack at https://elixir.bootlin.com/linux/v4.4.90/source/net/ipv4/tcp.c#L2401 . However, I do not know where the source code the Nagle Algorithm is implemented in kernel. If you know, could you please help me? Brs, Naruto

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Why are the PAGE_SIZE and the physical page frame size different in x86_64 kernel?
by Hao Lee March 30, 2018

March 30, 2018

Hi, I'm confused about the meaning of the PAGE_SIZE macro in x86_64 kernel. Its value is 4KB and I once thought it was the size of a physical page frame, but now I think I'm wrong. I find that most of the physical address space is mapped by PMD entries, which means the actual physical page frame size is 2MB. Could someone explain why the PAGE_SIZE is not 2MB in x86_64 kernel? Thanks! Regards, Hao Lee

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V4l2 Sensor driver and Bridge Driver
by MUHAMMED ASAD P T March 30, 2018

March 30, 2018

Hi All, Need to write the Sensor driver. I have the below doubts: 1. What are the dependencies between the bridge driver and Sensor driver? 2. To write the sensor driver, what are the things, we need to look in bridge driver? 3. What are the Sensor driver functions called from bridge driver. 4 . What are the things the bridge driver expect from Sensor driver? -Thanks. Thanks & Regards - Asad IQ Root Technologies

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Need to write the Sensor driver
by MUHAMMED ASAD P T March 30, 2018

March 30, 2018

Hi All, Need to write the Sensor driver. I have the below doubts: 1. What are the dependencies between the bridge driver and Sensor driver? 2. To write the sensor driver, what are the things, we need to look in bridge driver? 3. What are the Sensor driver functions called from bridge driver. 4 . What are the things the bridge driver expect from Sensor driver? Thanks & Regards - Asad IQ Root Technologies

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where is __percpu_seg initialized?
by 落痕 March 28, 2018

March 28, 2018

Hi all: I knew the kernel implement the per-cpu variable via __percpu_seg. For example on x86 architecture, it's defined as: #ifdef CONFIG_X86_64 #define __percpu_seg gs #define __percpu_mov_op movq #else #define __percpu_seg fs #define __percpu_mov_op movl #endif But I'm curious where __percpu_seg is initialized?? I fail to find the relative code. Thanks.

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Writing a Line discpline driver to talk to a stm32 controller
by Oliver Graute March 26, 2018

March 26, 2018

Hello list, I have a imx6ul connected to a stm32 controller via a serial interface. I need to implement a little protocol to talk towards the stm32 controller for send and receive ontop of the serial line. I found out that I have to write my own line discpline driver for doing this. After digging around in drivers/tty/n_* I have a little idea what to do here. I already attached my demo ldisc to a /dev/ttymxc7 via the ldattach command in userspace. This looks fine so far. Here my first Questions: Is there a way to permanent attach the ldisc to an serial interface in the Kernel? I have a reset GPIO to reset the stm32 controller. I would like to toggle this GPIO on opening the device. But the open() method in the ldisc driver seems the wrong place to do this. But in which open() should I do this? the underlying serial imx.c driver do not have any open() and I'am using this driver also for other serial lines? useful links to the ldisc topic: https://www.kernel.org/doc/Documentation/serial/tty.txt http://www.embeddedlinux.org.cn/essentiallinuxdevicedrivers/ Best Regards, Oliver

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A question about function split_mem_range
by Hao Lee March 25, 2018

March 25, 2018

Hi, I'm currently reading the memory management source code and get stuck on a function. In arch/x86/mm/init.c, there is a function called split_mem_range[0]. Its logic is very complicated and I can't figure out what it does. I have added some debug statements in this function to print all variable, but I still can't understand it. I have also searched it on Google and couldn't find any helpful articles. Could someone give me some help about what on earth this function does? Many thanks! [0] https://github.com/torvalds/linux/blob/bcfc1f4554662d8f2429ac8bd96064a59c14… Regards, Hao Lee

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Linux kernel Books
by vish chopra March 25, 2018

March 25, 2018

Hi, IA-64 Linux Kernel: Design and Implementation (Hewlett-Packard Professional Books)is a good book to learn linux internal or not? Regards, Vishal Chopra

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