March 2014 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

module usage count
by J.Hwan Kim March 4, 2014

March 4, 2014

Hi, everyone When I use /proc file system in communicating between kernel and user space, is the usage count of moudule automatically incremented or decremented? I register proc file via create_proc_entry() and use .open, .close and .mmap not using .read and .write function. Please give me any hint.. Thanks in advance Best Regards, J.Hwan Kim

3 2

Device Tree support for x86_64 kernel? Unresolved symbol apic_force_enable
by Bob Paauwe March 3, 2014

March 3, 2014

Background: I'm working on a project that needs device tree like capability. Using the device tree OF driver works well and I don't want to create something that closely duplicates that functionality. When building a 32bit kernel, all works fine. However when building a 64bit kernel, the linking stage fails with an unresolved symbol: apic_force_enable This symbol is getting called from arch/x86/kernel/devicetree.c and is defined in arch/x86/kernel/apic/apic.c but only when !CONFIG_X86_64 I see two possible fixes but as I'm unfamiliar with this area of the kernel I don't know which would be a better choice. 1) in arch/x86/kernel/apic/apic.c, define the apic_force_enable() function in the X86_64 bit path and have it return 0. Something like: int __init apic_force_enable(unsigned long addr) { return 0; } 2) wrap the call to apic_force_enable with a #ifndef CONFIG_X86_64 in devicetree.c. Something like : #ifndef CONFIG_X86_64 if (apic_force_enable(r.start)) return; #else return; #endif I've been using #1 successfully in my development and it seems like it would be the best choice long term. I'm looking for some validation that this makes sense and if so, I'll submit a patch to lkm with the fix.

1 0

where is the module reference count incremented or decremented ?
by Jeong-Hwan Kim March 3, 2014

March 3, 2014

Hi, everyone When the module is communicating with user through /proc file system, where is the module reference count incremented or decremented in kernel source? Thanks in advance. Best Regards, J.Hwan Kim

2 2

Reset due to emergency remount r/o
by Priyaranjan Das March 3, 2014

March 3, 2014

Hi All, I am facing an kernel restart due to emergency remount. Could anybody tell me general techniques to go head with the debugging? Below are the logs which are seen during a reboot. [ 425.832395,1] SysRq : Emergency Remount R/O [ 425.876210,1] EXT4-fs (mmcblk0p36): re-mounted. Opts: (null) [ 425.925899,1] EXT4-fs (mmcblk0p33): re-mounted. Opts: (null) [ 425.928731,1] EXT4-fs (mmcblk0p29): re-mounted. Opts: (null) [ 425.955762,1] Emergency Remount complete [ 426.187136,0] Restarting system with command 'bootloader'. [ 426.187327,0] Current task:init(1) Parent task:swapper/0(0) [ 426.187430,0] Going down for restart now Regards, Priyaranjan

7 6

LF GSoC page
by Sima Baymani March 2, 2014

March 2, 2014

Hi Till, I'm guessing you're the author of this http://www.linuxfoundation.org/collaborate/workgroups/gsoc/2014-gsoc-kernel… which points to #kernelnewbies. Right now there are a lot of people coming in and asking for info or help etc. It would be helpful if you could add some more detail there. For example Greg K-H has stated he's the one to ping (or email, according to himself) - that could be something to add. Also, as far as I understand, applicants have to have an idea/suggestion of their own for projects (according to chats by Greg). Could you add information about that as well? Right now everybody else in that channel are more or less clueless, which imo isn't a good first impression for applicants =) BR, Sima

2 3

understanding register layout
by sham pavman March 2, 2014

March 2, 2014

Hi all, While going through the BCM 57712 code i found the following. /* [RW 32] reset reg#2; rite/read one = the specific block is out of reset; * write/read zero = the specific block is in reset; addr 0-wr- the write * value will be written to the register; addr 1-set - one will be written * to all the bits that have the value of one in the data written (bits that * have the value of zero will not be change) ; addr 2-clear - zero will be * written to all the bits that have the value of one in the data written * (bits that have the value of zero will not be change); addr 3-ignore; * read ignore from all addr except addr 00; inside order of the bits is: * [0] rst_bmac0; [1] rst_bmac1; [2] rst_emac0; [3] rst_emac1; [4] * rst_grc(global register); [5] rst_mcp_n_reset_reg_hard_core (global * register); [6] rst_mcp_n_hard_core_rst_b(global register); [7] * rst_mcp_n_reset_cmn_cpu(global register); [8] * rst_mcp_n_reset_cmn_core(global register); [9] rst_rbcn; [10] rst_dbg; * [11] rst_misc_core(global register); [12] rst_dbue (UART)(global * register); [13] Pci_resetmdio_n(global register); [14] * rst_emac0_hard_core; [15] rst_emac1_hard_core; 16] rst_pxp_rq_rd_wr; 17] * rst_atc; 18] rst_cnig; 19] rst_pglc (global register); 31:20] reserved */ Here is what i understand and here is what i need help with! What I understand, REG2 has 20 bits and what each of those bits signify, I understand. I also understand that if I read/write 1, it means that particular block has finished reset. If I read/write 0, it means that particular block has completed reset. But what is this addr 1-set, addr 2- clear and friends?

1 0

Completely Fair Scheduler - Min_vruntime
by Anup Buchke March 1, 2014

March 1, 2014

Hi all, I am trying to learn CFS. I came across this variable. min_vruntime : kernel documentation says it stores the total work done by the system . AND it is used to add new tasks more to the left in the rbtree so that they are scheduled quickly. But I am not able to understand why we need that variable and how it is used for 1. new added tasks 2. Tasks that wake up after sleep. I tried learning from professional linux kernel architecture+utlk and alike. But I am not able to understand. Also the key in the rbtree is used as (current_vruntime - min_vruntime) ? why are we even using such formule in which we subtract min_vruntime which is monotonically increasing?? I think it is related to some latency period and the processes which runs in one latency period. I think I may be missing some of the core concepts on scheduling process, but not able to figure out what I am missing. My understanding is pretty messed up the use of min_vruntime. I would be highly grateful if someone could explain me in bit of a detail about my answer. Thanks in Advance!!! Anup

1 0