Marcus Folkesson

Embedded Linux Artist

GPLv2 and GPLv3

Open Source "Free as in freedom - not as in free beer". Free beer is nice, but freedom is even nicer. I have been working with companies from different sections including consumer electronics, military applications, automotive and aeronautics. One common question, regardless of section, is "Can we really use Open Source in our product?". The answer is usually Yes, you can, but.... One common misunderstanding is to interpret Open Source as in free beer.

Posted by Marcus Folkesson on Thursday, February 10, 2022

ath10k QCA6584 and Wireless network stack

ath10k QCA6584 and Wireless network stack ATH10K is the mac80211 wireless driver for Qualcomm Atheros QCA988x family of chips, and I'm currently working [1] with the QCA6584 chip which is an automotive graded radio chip with PHY support for the abgn+ac modes. The connection interface to the chip is SDIO which is hardly supported for now, but my friend and kernelhacker, Erik Strömdahl [2] , has got his hands dirty and is currently working on it.

Posted by Marcus Folkesson on Wednesday, April 4, 2018

Linux driver for PhoenixRC adapter

Linux driver for PhoenixRC adapter Update: Michael Larabel on Phoronix has written a post [3] about this driver. Go ahead and read it as well! A few years ago I used to build multi rotors, mostly quad copters and tricopters. It's a fun hobby, both building and flying is incredible satisfying. The first multi rotors i built was nicely made with CNC cutted details. They looked really nice and robust.

Posted by Marcus Folkesson on Saturday, March 17, 2018

get_maintainers and git send-email

get_maintainers and git send-email Many with me prefer email as communication channel, especially for patches. Github, Gerrit and all other "nice" and "user friendly" tools that tries to "help" you to manage your submissions does not simply fit my workflow. As you may already know, all patches to the Linux kernel is by email. scripts/get_maintainer.pl (see [1] for more info about the process) is a handy tool that takes a patch as input and gives back a bunch of emails addresses.

Posted by Marcus Folkesson on Sunday, January 7, 2018

OOM-killer

OOM-killer When the system is running out of memory, the Out-Of-Memory (OOM) killer picks a process to kill based on the current memory footprint. In case of OOM, we will calculate a badness score between 0 (never kill) and 1000 for each process in the system. The process with the highest score will be killed. A score of 0 is reserved for unkillable tasks such as the global init process (see [1]) or kernel threads (processes with PF_KTHREAD flag set).

Posted by Marcus Folkesson on Friday, December 1, 2017

printk()

printk() So, a week in Prague has come to its end. The Embedded Linux Conference Europe was this year co-located with Open Source Summit and offered a lot of interesting talks on various topics. One of the hottest topics this year was about our most beloved debugging function - prink(). What is so hard with printing? It turns out that printk is quite deadlock-prone and that is not an easy thing to work around in the current infrastructure of the kernel.

Posted by Marcus Folkesson on Thursday, November 2, 2017

Memory management in the kernel

Memory management in the kernel Memory management is among the most complex parts in the Linux kernel. There is so many critical parts such as page allocator, slab allocator, virtual memory handling, memory mapping, MMU, IOMMU and so on. All these parts has to work perfect (or at least allmost perfect :-) ) because all system do use them either they want to or not. If there is a bug or performance issue you will be noticed quite soon.

Posted by Marcus Folkesson on Wednesday, September 27, 2017

MMAP memory between kernel and userspace

MMAP memory between kernel and userspace Let kernel allocate memory and let userspace map is sounds like an easy task, and sure it's. There are just a few things that is good to know about page mapping. The MMU (Memory Management Unit) contains page tables with entries for mapping between virtual and physical addresses. These pages is the smallest unit that the MMU deals with. The size of a page is given by the PAGE_SIZE macro in asm/page.

Posted by Marcus Folkesson on Wednesday, September 27, 2017

PID1 in containers

PID1 in containers What is PID 1 The top-most process in a UNIX system has PID (Process ID) 1 and is usually the init process. The Init process is the first userspace application started on a system and is started by the kernel at boottime. The kernel is looking in a few predefined paths (and the init kernel parameter). If no such application is found, the system will panic().

Posted by Marcus Folkesson on Wednesday, September 27, 2017

2.2" TFT display on Beaglebone

2.2" TFT display on Beaglebone I recently bought a 2.2" TFT display on Ebay (come on, 7 bucks...) and was up to use it with my BeagleBone. Luckily for me there was no Linux driver for the ILI9341 controller so it's just to roll up my sleeves and get to work. Boot up the BeagleBone I haven't booted up my bone for a while and support for the board seems

Posted by Marcus Folkesson on Sunday, August 27, 2017

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