July 2012 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Finding the interrupt vector of a given IRQ
by Mark Farnell Oct. 20, 2012

Oct. 20, 2012

In the kernel, how can I find out the interrupt vector number of a given IRQ (for example, IRQ7)? Within the kernel module, I would like to manually set the IRQ using the assembly code: asm("int $<irq vector>"); and let the IRQ handler installed by a different module catch that interrupt. Is this possible? Thanks! Mark

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Writing I2C chip driver in combination with other structure
by aurum spark Sept. 4, 2012

Sept. 4, 2012

Hi All, I have written and seen lot of code of i2c drivers for input subsystem devices and much familiar with that. Now I have started writing driver for one chip that is not exactly type of input device. So, little bit confused about how should be the driver architecture so that it will be a clean code yet simple. Following text and diagram explains short functional description of chip. Chip Interface :- ========== ====== ======= | | | I2C | | | ----- I2C --- | Device | | ARM | ----- Bus -- | With rw | ------------ Input Connect | | | regs | | | ---------------| | ====== INTR ======= So above picture depicts how chip is interfaced to ARM CPU. This chip has some registers which are rw and can be used to read certain information from chip or to program it. This chip is capable of giving intterupt to CPU. This chip has one input which it like some cable connection. It detects when this cable is connected and raises the interrupt. Functionality Expected in Driver:- =================== 1. Driver should communicate with chip over I2C. 2. Driver should report event to user space upon receiving interrupt from I2C device. 3. Driver should be capable of programming I2C chip @ the time of initialization as well should be capable of changing registers as and when Linux User Space application wants to. What I have thought of:- ============== #1 definitely makes this as i2c client driver(chip driver) #2 Here I have few options a) Shall I use input subsystem mechanism to report interrupt as an event to user space ? In this case it's combination of I2C + input subsystem. Then application can read something over i2c and decide next flow, OR b) Shall I use some sysfs based interface on which application can do select sys call and can receive event ? for this nothing extra required. #3 Since approach in #2 is not fixed here also there are multiple options a) This can be written as I2C client + char driver so that it can have ioctls to send commands to i2c chip based on applications demand. b) We can provide sysfs interface to user space to send commands to i2c device as and when required at runtime. As per my thoughts I am not sure shall I make this as input device just to report one event upon getting interrupt from device. Also will it be ok to have this as char driver in combination with i2c chip driver ? Please guide me and take me to correct source or documentation or to source code of some driver for this kind of device. Does i2c support ops like fbops ? Regards, ~/Aurum

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Porting my BSP to higher Kernel Versions
by Ramya Desai Aug. 24, 2012

Aug. 24, 2012

Dear Experts, I have a working BSP which runs on Kernel 2.6.10. Now I wanted to upgrade my BSP to higher versions like, 2.6.24. Is there any documentation/steps available to do so? Regards, Ramya

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arm L_PTE_XXX entry addition for Debugging purpose
by Dhyan Aug. 2, 2012

Aug. 2, 2012

Dear All, >From linux(2.6.35) arm page table architecture i can see we have one hardware page table and there is corresponding Linux page table Entry (L_PTE_*).The "Linux" PTE definitions are as like below from arch/arm/include/asm/pgtable.h. #define L_PTE_PRESENT (1 << 0) #define L_PTE_FILE (1 << 1) #define L_PTE_YOUNG (1 << 1) #define L_PTE_BUFFERABLE(1 << 2) #define L_PTE_CACHEABLE (1 << 3) #define L_PTE_USER (1 << 4) #define L_PTE_WRITE (1 << 5) #define L_PTE_EXEC (1 << 6) #define L_PTE_DIRTY (1 << 7) #define L_PTE_COHERENT (1 << 9) #define L_PTE_SHARED (1 << 10) So is it possible to add one more #define L_PTE_DEBUG (1 << 11) for my debugging purpose (basically to trap all the write to that page and set this bit when write happens and clear it off in another thread )? Or is there any limitation like we can use only L_PTE till 10th bit ? So could you please help -- Thanks & Regards Dhayn

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system stucks in run_init_process
by Rahul Bedarkar Aug. 1, 2012

Aug. 1, 2012

Hi, I have disabled CONFIG_DEVTMPFS in kernel config and system stucks in run_init_process call which is called after freeing initmem. Any idea why this is happening. If devtmpfs is enabled, it runs normally. I am using 3.3.2 kernel. Thanks, Rahul B.

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netdev architecture question
by Daniel Ng July 31, 2012

July 31, 2012

Hi, I'm planning a network driver that uses netdev queues. On the Rx side, I wish to do some further processing of incoming skbs that have been dequeued from the netdev queues. Is it possible for the skb to remain on the queue after it has been received, so that I don't have to put it into yet another queue/buffer to do the further processing? ie. I wish to process the received packet while it is still in the netdev queue. Is this possible? Is it even a good idea? Cheers, Daniel

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KVM nested virtualization: guest ioctl calls
by siddhesh phadke July 30, 2012

July 30, 2012

Resending with subject. I am newbie in nested KVM virtualization and I am trying to understand the code for nested virtualization. I am not able to understand how nested guest's ioctl calls are intercepted by KVM.Does each ioctl of nested guest is intercepted by L0 or it is passed to L1? Can anyone please help me with this or correct me if I am totally off the track?

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(no subject)
by siddhesh phadke July 30, 2012

July 30, 2012

I am newbie in nested KVM virtualization and I am trying to understand the code for nested virtualization. I am not able to understand how nested guest's ioctl calls are intercepted by KVM.Does each ioctl of nested guest is intercepted by L0 or it is passed to L1? Can anyone please help me with this or correct me if I am totally off the track?

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Difference between user space drivers and kernel space drivers
by Manu Gupta July 30, 2012

July 30, 2012

Hi All, I have been trying to figure out the difference between user space drivers and kernel space drivers. I have a few questions 1. What are user space drivers? 2. How are they beneficial and when are they usually used? -- Regards Manu Gupta

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Re: orphan process is causing deadlock in __kernel_vsyscall ()
by Sri Ram Vemulpali July 26, 2012

July 26, 2012

> Hello All, > > I am debugging a problem which I do not know how to solve. I know what > is happening, but cannot find solution to it. If anyone has any > suggestions or solution that would be really grateful and I appreciate > it. > > Here is the description. > > I have a thread which spawns a child process using fork() and in child > context it execv to shell and parent thread waits on waitpid(). This > child process is nothing but a shell /bin/sh, so that from program I > can create shell and run some commands. > In this shell instance, I run tshark for capturing network traffic. I > have really high traffic going, so system is really busy. All is good > so far, but when I send SIGKILL to child process (shell) from another > thread from same application, > child process (shell) gets terminated and tshark is assigned to > init(1) process as orphan. The parent thread which spawned the child > process unblocks from waitpid() after cleaning child instance and > continues it execution. > > Here is the problem: > Once the parent thread resumes from waitpid(), it hits fprintf to > print message "exiting from shell" to console. In here the main thread > gets blocked in __kernel_vsyscall () entered from fprintf. Following > is my stack trace from gdb. > But after some more debugging and found that, if I kill from another > shell "tshark" process which is assigned to init(1) as child, the > parent thread unblocks from __kernel_vsyscall (). > > Can anyone tell what is going on, is this related to futex spinning > problem where lock is been held by tshark. How would I approach this > problem? > Or is there a way to kill all child process of a process without > making them orphan. Because when a child process is running at the > time parent is exiting, that child process is assigned to init(1) as > orphan process. > Can this behavior be modified. Please let me know any suggestions and > thoughts. Thanks in advance. > > -- > Regards, > Sri. > > (gdb) backtrace > #0 0xffffe424 in __kernel_vsyscall () > #1 0xb7e6396b in write () from /lib/libc.so.6 > #2 0xb7e0c2ef in _IO_new_file_write () from /lib/libc.so.6 > #3 0xb7e0bf93 in new_do_write () from /lib/libc.so.6 > #4 0xb7e0c296 in _IO_new_do_write () from /lib/libc.so.6 > #5 0xb7e0ce20 in _IO_new_file_overflow () from /lib/libc.so.6 > #6 0xb7e0c0cd in _IO_new_file_xsputn () from /lib/libc.so.6 > #7 0xb7de3634 in vfprintf () from /lib/libc.so.6 > #8 0x09ad62a2 in acme_fprintf (stream=0xb7ee2560, > format=0x9f17694 "shell exited. returning to acli\n") > at /home/svemulpali/cc/svemulpali_SCOTTY_main/linux/private/common/src/coutOverride.cpp:42 > #9 0x094a9345 in vxShellCmdStartWait (syscmd=0x0) > at /home/svemulpali/cc/svemulpali_SCOTTY_main/linux/private/lib/stub/vxShellLib.cpp:210 -- Regards, Sri.

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