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

SRIO maintenance read hangs (mpc8548)
by shrikant hegde Aug. 4, 2011

Aug. 4, 2011

Hi all, I am working on srio; When i tried to send maintenance packet to switch it hangs. Symptom when i tried to read DIDCAR of switch,( i.e read 0x8000_0000 ), or HDIDLOCK (0x8000_0068 ), execution of code hangs; if i press break in code warrior its coming out with an error. register value dump EPWISR 0x80000000 -- physical or logical/transport error interrupt LTLEDCSR 0x08000000 -- illegal transaction decode, received request/response packet LTLCCCSR 0x82000000 Below are my system detail: Processor mpc8548 and Tsi578 switch. Processor is connected to switch on same board.I have written standalone code (no OS) to exercise srio, using code warrior. Processor side configurations Its configured to 1x, 2.5gbs, host. law and tlb are configured. 0x8000_0000 0x8FFF_FFFF maintenance window configured 0x8000_0000 0x8000_0FFF (4k) switch side configuration 1x,2.5gbs, swap disabled (configured during POR) Processor side link training bit is setting. Am I missing any configuration , in switch side or processor side ? Any pointer is very helpful. Forgive me if its a wrong forum to post srio queries. thanks shrikant -- View this message in context: http://old.nabble.com/SRIO-maintenance-read-hangs-%28mpc8548%29-tp30949266p… Sent from the kernelnewbies mailing list archive at Nabble.com.

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Unable to remove kernel module showing permanent using lsmod
by sakthi selvam April 17, 2011

April 17, 2011

Dear All, Need your assistance: Currently I am using Wind River Linux distribution OS with kernel version 2.6.27.39 and Wind River version pne-3. After loading of my kernel module, I found it was permanent in the kernel using lsmod (for ex see below Ref 1). When I tried to remove, it was displaying as “ERROR: Removing 'hsl_module': Device or resource busy”. For your information, the same module is working fine with the Wind River pne-2 Linux Distribution OS with kernel version 2.6.21. >From the kernel source, I came to know that only possibility of showing permanent is “if there is non-availability of cleanup_module and with the availability of init_module”. But in my case, cleanup module also available in memory, after loading the module. I used to check using the file in /proc/kallsyms for the availability of cleanup module in memory. Thanks for reading. Prompt reply is expected to identify the root cause. Ref 1: Module Size Used by hsl_module 530454 0 [permanent] Thanks, Sakthi Selvam

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Snooping on sockets/file descriptors
by Vimal April 4, 2011

April 4, 2011

Hi, Is it possible for an application (say "snoop", with sufficient privileges) to monitor data on any socket/file descriptor in the system? Here's an example: suppose we have a browser and it creates a tcp socket to connect to a URL. Whenever the browser issues a read() and data is pushed to user space, I want "snoop" to get notified and made available a copy of the same data that the browser read. ptrace can be used to do it, but then there are several ways the app can read data. It could use read(), or recv() or recvmsg(). Is there a better way to deal with this complexity? It's like the action of "tee" on any socket/file descriptor in the system. -- Vimal

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linux gpio
by Jürgen Lambrecht April 4, 2011

April 4, 2011

Hello, I am new to linux (coming from eCos). My backlight driver does not start up because the reset gpio pin is not correct specified. How does gpio work in Linux? I have 2 platforms that use the same backlight driver, under arm, for freescale imx: imx31_3ds and imx27_3ds. I don't think that matters, I just need to understand the linux gpio. The imx31 platform gives the number 88 as gpio number to the backlight driver. That number comes out of 'iomux-mx3.h'. In 'iomux-mx27.h' the GPIO's are specified in an other way, the "hardware" way, specifying bank and port. I think Linux GPIO needs a sort of general gpio number. But how do I calculate that number out of the datasheet? In the imx31 datasheet, I cannot find that number 88 (or the other numbers in 'iomux-mx3.h'). Kind regards, Jürgen -- Jürgen Lambrecht R&D Associate Tel: +32 (0)51 303045 Fax: +32 (0)51 310670 http://www.televic-rail.com Televic Rail NV - Leo Bekaertlaan 1 - 8870 Izegem - Belgium Company number 0825.539.581 - RPR Kortrijk

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Re: ARM : Kernel : Setting up of MMU in head.S
by Dave Hylands April 3, 2011

April 3, 2011

Hi Prakash, On Wed, Mar 30, 2011 at 11:01 PM, Prakash K.B. <prakashk75(a)gmail.com> wrote: > Merci mate. :-) > > On Thu, Mar 31, 2011 at 3:59 AM, Dave Hylands <dhylands(a)gmail.com> wrote: >> >> Hi Prakash, >> >> On Wed, Mar 30, 2011 at 2:35 PM, Dave Hylands <dhylands(a)gmail.com> wrote: ...snip... >> When the MMU table is turned on, the PC is still at 0x800xxxx, so even >> though the kernel has 0xc00xxxxx mapped to 0x800xxxxx it also has to >> have 0x800xxxxx mapped to 0x800xxxxx. > > [Prakash] I think you meant to say "So even though the kernel intends to map > 0xc00XXXX to 0x800XXX in the future, it has currently mapped 0x800xxx to > 0x800xxx. No. the create_page_table function creates a page table which has 0x800xxxxx and 0xc00xxxxx both mapped to 0x800xxxxx. The one store intrustion saves the identity mapping (for 1 Mb) and the loop sets up the 0xc00xxxxx to 0x800xxxxx mapping. The identity portion is used as we discussed, and a few instructions after turning on the MMU, the CPU then does a jump from the 0x800xxxxx space to the 0xc00xxxxx space. After that, the identity mapping is no longer needed. Shortly after this, head.S calls into the start_kernel function (from init/main.c) and the paging_init function reinitializes the MMU removing the identity mapping. > > Now that I know this identity mapping is done on purpose, I hope to make > good progress with the succeeding sequence. > > Do you confirm that only one entry is written into this L1 table because > both mmu_enable and enable_mmu_end are on the same section? Yeah - essentially, that one mapping entry covers 1Mb of code space, which is sufficient to cover all of head.S, which is always at the front of the kernel image. -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com

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GSoC project idea: HFS Plus journal
by Naohiro Aota April 2, 2011

April 2, 2011

Hi, I see some of you are talking about GSoC participation. I'm also thinking of it. I have MacBookPro booting both MacOSX and Linux. Now Linux can write the filesystem safely only when HFS Plus journal is off. My life would be more better if Linux have complete HFS Plus filesystem read/write support. So I'm thinking of implementing HFS Plus Journal support on Linux. I've searched and found a technote about HFS Plus format describe its Journal [1]. How do you think about it? Regards, Naohiro [1] http://developer.apple.com/library/mac/technotes/tn/tn1150.html#Journal

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Debug Kernel Crash
by swathi suresh April 1, 2011

April 1, 2011

Hello All, I wanted to know what is the best way to generate the kernel crash dump on kernel panic, after doing some searching, i came to know we can use kexec to load a new kernel on the kernel, i followed the instruction from the following links http://www.dedoimedo.com/computers/kdump.html http://www.developertutorials.com/tutorials/linux/reboot-linux-faster-07220… I do found that the kernel load properly with the, kexec -l option followed by kexec -e option, but when i set the kernel to be loaded on kernel panic using the option kexec -p, i see that after kernel crash, the system just hangs, it wont even try to load the new kernel. following are the commands am using. Can some one point, if there is any thing wrong with this. chkconfig kdump on /etc/init.d/kdump start kexec -l --append="`cat /proc/cmdline`" --initrd=/boot/initrd.img-2.6.35.10-kdump /boot/vmlinuz-2.6.35.10-kdump kexec -e works fine and loads the kernel successfully, i will be able to see *starting new kernel* in the shell * * * chkconfig kdump on /etc/init.d/kdump start * kexec -p --append="`cat /proc/cmdline`" --initrd=/boot/initrd.img-2.6.35.10* -kdump ** /boot/vmlinuz-2.6.35.10 -kdump * * * i simulate the panic by using echo 1 > /proc/sys/kernel/sysrq echo c > /proc/sysrq-trigger which just crash the kernel and system hangs, and it does not show any message *starting new kernel.* * * Thanks,

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mapping address pointer to page structure
by swathi suresh March 31, 2011

March 31, 2011

Hi All, Is it possible to map a address like skb->data in to struct page. My requirement is to convert multiple skb to a single master skb, having all the data of other skb. i.e, i want add skb->data of multiple skb to a single skb as the fragments. So instead of making a memcpy every time, i just call skb_add_rx_frag my requirement is some thing like this *.* *.* *struct page *page = virt_to_page(skb->data);* * * *skb_add_rx_frag(master_skb, skb_shinfo(master_skb)->nr_frags, page, off, skb->len)* *.* *.* And can some one please tell what is the use of the functions like * virt_to_page* and *kmap_atomic_to_page*, i tried calling virt_to_page(skb->data), but when i print the data in the page address ( page_address(page) ) and the data in pointed by skb->data, i came to know its mapping to a wrong page. so can some one please explain me what is correct way to do this. Thanks in advance.

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[virtual memory] page_table_lock & mmap_sem
by Venkatram Tummala March 31, 2011

March 31, 2011

Hi, Why do we need both page_table_lock & mmap_sem in the kernel. Why isn't mmap_sem good enough for serialization. As far as i see it, all attempts to change the page table hierarchy in the kernel is done after holding the write lock on mmap_sem. As we are already holding the write lock, we do we need an extra page_table_lock (spinlock) ? Are there any code paths in the kernel which attempt to modify the page table hierarchy without holding the write lock on mmap_sem ? page_table_lock is a finer grained lock than mmap_sem but page_table_lock is only taken after holding a write lock on mmap_sem (as far as i can tell). What is the reasoning behind having an extra spinlock? Thanks. Venkatram Tummala

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ARM : Kernel : Setting up of MMU in head.S
by Prakash K.B. March 31, 2011

March 31, 2011

Hello. Please do not hesitate to let me know if this must be posted elsewhere. I have been trying to understand the code that sets up the MMU. I do have a fair understanding of the way MMU is meant to be setup, but something in the kernel code is tripping me. The code that kickstarts setting up of MMU is __create_page_tables in /arch/arm/kernel/head.S. This code is position independent. It basically - Reserves 16KB of memory in RAM just before the start of the uncompressed kernel. - Clears the 16KB meant to serve as L1 lookup table containing 4096 entries - Creates a section entry in L1 table for the kernel code to be mapped into physical memory It is this creation of section entry code that is puzzling me. The index used to program this entry is based on physical address of the kernel base. The way it ought to work is this. When the CPU issues a virtual address, the top bits are used as an index into this L1 table and then through a couple of table walk throughs, the physical address is arrived at. So the index used to program the L1 table ought to have been Now look at this code. __create_page_tables: pgtbl r4 @ page table address /* * Clear the 16K level 1 swapper page table */ mov r0, r4 @r0 = 0x80004000 mov r3, #0 add r6, r0, #0x4000 @r6 = 0x80008000 1: str r3, [r0], #4 str r3, [r0], #4 str r3, [r0], #4 str r3, [r0], #4 teq r0, r6 bne 1b /* r10 contains proc_info pointer */ ldr r7, [r10, #PROCINFO_MM_MMUFLAGS] @ mm_mmuflags /* * Create identity mapping to cater for __enable_mmu. * This identity mapping will be removed by paging_init(). */ adr r0, __enable_mmu_loc ldmia r0, {r3, r5, r6} sub r0, r0, r3 @ virt->phys offset add r5, r5, r0 @ phys __enable_mmu add r6, r6, r0 @ phys __enable_mmu_end mov r5, r5, lsr #20 mov r6, r6, lsr #20 1: orr r3, r7, r5, lsl #20 @ flags + kernel base str r3, [r4, r5, lsl #2] @ identity mapping teq r5, r6 addne r5, r5, #1 @ next section bne 1b The 2 lines above 1: orr r3, r7, r5, lsl #20 @ flags + kernel base ==> Correct str r3, [r4, r5, lsl #2] @ identity mapping ==> ?? create a section entry using index based on physical address. Am I missing something here? Regards, Prakash

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