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calculating ring buffer size
by Amit Nagal Oct. 17, 2011

Oct. 17, 2011

Hi , While going through a few usb drivers code , i observed that the drivers maintain a ring buffer which stores data coming from usb device in interrupt context . Also these ring buffers is a power of 2 size i am looking for reasons how to compute the the max size of these ring buffers , so that no overflow situation happens . What factors should always be accounted while computing the max size of these ring buffers . Regards Amit Nagal

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sample USB Driver / Probe not getting called
by Abhijit Pawar Oct. 17, 2011

Oct. 17, 2011

Hi All, Is there any way to call a sample USB driver whenever a USB device is attached to the system irrespective of the class and type of the device? To do this, LDD3, chap 13 mention that for USB device table, we only need to add the driver_info entry as 42. However if I do this, my probe is never getting called. Now, I give the vendor and product id of this Mouse to the device_id table and load my driver again. Still the probe is not getting called. Is it that USB core is getting the proper driver for this mouse before my driver entry in the list? Am I missing something? Regards, Abhijit Pawar

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power profiling ( /proc/acpi/processor .. missing)
by pankaj singh Oct. 17, 2011

Oct. 17, 2011

Hi, I am trying to do power profiling of my laptop (DELL LATITUDE) where i am using ubuntu 11.10. For this i m using powertop and acpitool but unfortunately i am not able to get C and P states. when i run `acpitool -c` it says Function Show_CPU_Info : could not read directory /proc/acpi/processor/ Make sure your kernel has ACPI processor support enabled. I have already check the config file ACPI_PROCESSOR is enable(in kernel). So do i require to install any specific driver to get C and P states. For information i m using kernel version 3.0.0-12-generic. -- Pankaj SIngh Phone No: 9921865080

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why does the 'break_lock' field of spinlock exist for preemptive kernel?
by Parmenides Oct. 16, 2011

Oct. 16, 2011

Hi, I am reading the source code of spinlock and have a question about it. The spinlock is defined as: typedef struct { volatile unsigned int slock; #ifdef CONFIG_PREEMPT unsigned int break_lock; #endif } spinlock_t; When 'break_lock' is one, it indicates that there are other tasks waiting the spinlock. If so, these tasks should be running on other CPUs. In other words, there are definitely no other tasks waiting the lock, which are on the same CPU on which the spinlock owner is runing, because the owner has disabled the kernel preemption. That is, there are no other local tasks which can set 'break_lock' to 1. Therefore, I think whether or not 'break_lock' is defined has nothing to do with CONFIG_PREEMPT. May be a misunderstanding. Any explanation?

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hello dick
by bob jonny Oct. 16, 2011

Oct. 16, 2011

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How to compile an older kernel?
by Parmenides Oct. 16, 2011

Oct. 16, 2011

Hi, I am using lfs which runs kernel 2.6.34, gcc 4.1.2 and ld 2.17. For some purposes, I want to compile the 2.6.11 kernel source. After doing some configuration, I did make which issues many warnings or error messages. For some of them: ... ... ... In file included from include/asm/mpspec.h:5, from include/asm/smp.h:18, from include/linux/smp.h:19, from include/linux/sched.h:25, from arch/i386/kernel/asm-offsets.c:7: include/asm/mpspec_def.h:78: warning: 'packed' attribute ignored for field of type 'unsigned char[6]' CHK include/asm-i386/asm_offsets.h UPD include/asm-i386/asm_offsets.h CC init/main.o ... ... ... In file included from include/asm/mpspec.h:5, from include/asm/smp.h:18, from include/linux/smp.h:19, from include/linux/sched.h:25, from arch/i386/kernel/process.c:17: include/asm/mpspec_def.h:78: warning: 'packed' attribute ignored for field of type 'unsigned char[6]' {standard input}: Assembler messages: {standard input}:909: Error: suffix or operands invalid for `mov' {standard input}:910: Error: suffix or operands invalid for `mov' {standard input}:1121: Error: suffix or operands invalid for `mov' {standard input}:1122: Error: suffix or operands invalid for `mov' {standard input}:1199: Error: suffix or operands invalid for `mov' {standard input}:1200: Error: suffix or operands invalid for `mov' {standard input}:1275: Error: suffix or operands invalid for `mov' {standard input}:1276: Error: suffix or operands invalid for `mov' {standard input}:1366: Error: suffix or operands invalid for `mov' {standard input}:1378: Error: suffix or operands invalid for `mov' make[1]: *** [arch/i386/kernel/process.o] Error 1 make: *** [arch/i386/kernel] Error 2 I think it is no problem to use newer compiler to compile older kernels. But, it seems that this is not really the case. To compile the 2.6.11 kernel, what do I need to adjust my system?

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Query on Rx Frame processing
by amit mehta Oct. 15, 2011

Oct. 15, 2011

I'm trying to understand Linux Network subsystem and after reading some documents, my broad level understanding for Rx Path is as follows: 1: Card receives the packet. 2: Assume everything is fine, the card DMAs the frame for the driver to process it further. 3: Driver allocate an skb buffer, adjusts the headroom. 4: Fills the buffer and pass it to the Network layer. Now in step 4 above, driver passes this packet to the network layer by calling netif_receive_skb() which may return NET_RX_DROP (packet was dropped), but most (I checked some of the network driver code) of the network drivers do not do this check. Hence, Q1: Shouldn't drivers be doing that ? Q2: Suppose the Card keeps pushing the frames at very high rate (10 Gig adapters are already in the market and maybe in near future we might have even faster ethernet adapters) then how the driver and the networking stack will handle such rapid frames arrivals? Will NAPI, interrupt coalescing be enough ? I'm referring kernel version 2.6.31 -Amit

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Why can the kernel be stuck by a busy kernel thread ?
by Parmenides Oct. 15, 2011

Oct. 15, 2011

Hi, I code a kernel module which do some nop. When inserted into the kernel, the kernel will be stuck and can not reponse my keypress anymore. So, I have to reboot to get out. Why? #include <linux/init.h> #include <linux/module.h> #include <linux/kernel.h> #include <linux/kthread.h> struct task_struct *ktask = NULL; static int thread_func(void *data) { int i; while (!kthread_should_stop()){ for (i = 0; i < 1000; i++){ asm volatile ("nop\n\t"); } } return 0; } static int tst_init(void) { ktask = kthread_run(thread_func, NULL, "mythread"); return 0; } static void tst_exit(void) { if (ktask){ kthread_stop(ktask); ktask = NULL; } } module_init(tst_init); module_exit(tst_exit); MODULE_LICENSE("GPL"); MODULE_AUTHOR("Parmenides"); MODULE_DESCRIPTION("Something.");

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Customized kernel and nVidia binary drivers
by Cihangir Aktürk Oct. 14, 2011

Oct. 14, 2011

Hi everybody, I am building custom kernels using "make-kpkg" command - the debian way, everything works great even my nVidia propriatery driver. And this nvidia module confuses me so much. When I build my kernel with standard "make", and install it as it is expected there is no nvidia module in my /usr/lib/kernel-ver directory and not surprisingly simply copying this driver from older kernel to a new one doesn't work as well. I wonder how can this nVidia binary driver still work if I compile my kernel with "make-kpkg"? What this utility does to make it happen?

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Fwd: How to avoid volatiles
by Srivatsa Bhat Oct. 14, 2011

Oct. 14, 2011

Forwarding to kernelnewbies list.. ---------- Forwarded message ---------- From: Prabhakar Lad <prabhakar.csengg(a)gmail.com> Date: Fri, Oct 14, 2011 at 3:35 PM Subject: Re: How to avoid volatiles To: Srivatsa Bhat <bhat.srivatsa(a)gmail.com> Hi, here you go Patch <http://patchwork.ozlabs.org/patch/115134/> Regards --Prabhakar On Fri, Oct 14, 2011 at 3:33 PM, Srivatsa Bhat <bhat.srivatsa(a)gmail.com>wrote: > > > On Fri, Oct 14, 2011 at 3:27 PM, Prabhakar Lad <prabhakar.csengg(a)gmail.com > > wrote: > >> Hi Srivatsa, >> >> I had a patch to submit but because of this issue its not being accepted. >> >> Regards >> --Prabhakar >> >> > Hi Prabhakar, > > Can you give a pointer (link) to your patch? > > Regards, > Srivatsa S. Bhat >

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