February 2013 - kernelnewbies@kernelnewbies.org

Kernel updating : export gpio not working ?
by Mylene Josserand Feb. 28, 2013

Feb. 28, 2013

Hi everyone ! I am currently updating the kernel of my company and I have some problems about gpios so I am asking you some help ! :) I think I am in the good mailist because it is the first time I update a kernel and a board configuration ! :D The previous kernel used was 2.6.31.14 and I am trying to update it to last stable version 3.7.9. In the previous kernel for a "home-made" board (with a IMx27 and a ARM9), we used these methods to export gpios in sysfs (for example for Gpio OUT) : mxc_gpio_mode(gpio_number | GPIO_GPIO | GPIO_OUT); gpio_request(gpio_number, name_of_gpio); gpio_export(gpio_number, 0); gpio_direction_output(gpio_number, gpio_value); In the sysfs, the gpio exported was visible under "name_of_gpio". Now, if I use the same methods, I can not get anything in sysfs except "gpiochip0, gpiochip32" etc. I tried to use these functions in a module and I could export a gpio but under "gpioXX" and not "name_of_gpio". Moreover, I tried to export a gpio using the sysfs interface. I succeeded to export it and set direction to "out" but when I try to set the value, it did not work and the value is always set to 0 (and this gpio was configured as OUT in the board). I make a diff about the gpio documentation and the old kernel used did not seem to have many differences with the new kernel ! There is only some methods added such as "gpio_resquest_one" and "gpio_export_link". I tried them without good results. What am I doing wrong ? What am I missing to make it work ? Is there some other configurations to add in the board configuration ? Thank you for any help/explanation ! -- Mylène JOSSERAND

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Kernel freeze when writing e1000 driver
by Phani Vadrevu Feb. 26, 2013

Feb. 26, 2013

Hi list, I am writing a network driver for the e1000 card. While doing the receive part, I saw that the kernel freezes whenever it reaches the netif_rx(skb) call. I was able to reproduce the same error when using a bare bones driver where I hard codde the skb data. Please see the code of that test function below. The data is that of a TCP packet (with IP and Ethernet headers). When I load the driver into a Virtual Machine, I see the VM process taking above 100% CPU in the host machine. The OS does not respond to input after this. If I comment out the netif_rx line it seems to be working fine. Thanks, Phani static void test_skb(void){ unsigned char t[] = {0x52,0x54,0x00,0x12,0x34,0x56,0x52,0x55,0x0a,0x00,0x02,0x02,0x08,0x00,0x45,0x00,0x00,0x2c,0x00,0x1c,0x00,0x00,0x40,0x06,0x62,0xa0,0x0a,0x00,0x02,0x02,0x0a,0x00,0x02,0x0f,0xc6,0x1a,0x1e,0xdb,0x4c,0x81,0x18,0x01,0x00,0x00,0x00,0x00,0x60,0x02,0x22,0x38,0x14,0x66,0x00,0x00,0x02,0x04,0x05,0xb4}; int len = 58; struct sk_buff *skb; skb = dev_alloc_skb (len + 2); if (skb) { printk("Allocated skb buffer\n"); memcpy(skb_put(skb, len), t, len); printk("step1\n"); //skb_put(skb, len); //skb->dev = dev; printk("step2\n"); //skb->protocol = eth_type_trans(skb, dev); skb->protocol = ETH_P_IP; printk("step3\n"); skb->ip_summed = CHECKSUM_UNNECESSARY; printk("step4\n"); //netif_rx (skb); printk("step5\n"); } printk(KERN_INFO"All Done"); if(skb){ dev_kfree_skb(skb); } }

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general_protection result to die
by horseriver Feb. 26, 2013

Feb. 26, 2013

hi; does general_protection trap necessarily result to die ? when executing this instruction : mov (%eax),%gs ,$ip turns to be general_protection. then it comes to debug() I have no clue for what has happend leads kernel to go here . it denotes what? Are there some adices here? thanks!

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valid address space ?
by Abu Rasheda Feb. 25, 2013

Feb. 25, 2013

I am trying to dump some kernel data structure (walk e.g. task or file data structure on x86_64 arch). Sometime accessing through a pointer, pointer may not be NULL, but pointing to invalid address due to garbage value. What I am looking for is range of address which are valid for kernel data structure. Is it correct to say following address are valid ? - Bit 0 - 47 are considered - Between FFFF8000'00000000 through FFFFFFFF'FFFFFFFF

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(no subject)
by Prasad Lakshman Feb. 25, 2013

Feb. 25, 2013

Hi , I am trying to implement own system call in Linux. Kernel version I chose is 3.5.7 I am following the steps from Linux Kernel Development 3rd edition. I got two problems with the implementation. 1.while trying to modify the code in kernel , there is no entry.S file for Intel x86 32 bit architecture. (my be i am missing some thing.) 2.while I am compiling user application with gcc I am getting error: unknown type name ‘helloworld’ my application is as follows #define __NR_helloworld 367 __syscall0(long, helloworld) int main () { printf("The helloworld system call is\n"; helloworld(); return 0; } I looked at Link [blog.163.com] which is given by Wanny but i could not find the solution,I could not locate syscall_table_32.s in my Linux source. Please help me in identifying the entry.S file for Intel x86 32 bit architecture in 3.5.7 kernel version sources,where i can make an entry for my system call into system call table. Help me in resolving error: unknown type name ‘helloworld’ in my application.

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Android - logger driver Help(Not sure if this is the right place)
by manty kuma Feb. 25, 2013

Feb. 25, 2013

Hi i want to know about event logs.. From this<http://elinux.org/Android_Logging_System>source i understood that event logs are in binary format. But how to read them? I mean i have the logger_entry structure pointer located inside memory. Using mmap, i am maping the pages to my address space and i am able to read the values inside the structure.. A field called msg contains the message of logcat and some other information as well. But for Event logs, the data is written in the binary format. From here<http://gitorious.org/android-eeepc/core/blobs/3e292b9716072cae37bff5b99c1d2…>, it is understood that the logs are somehow related to /system/etc/event-log-tags... My simple question is what is the format of the event log that is put inside the buffer? *Background* : logger_entry is the structure that is used by logger driver to maintain the buffer. Its field tell us from wher to start and what is the size of the bugger, etc.. *Purpose* : i dont have android running on the system when i want to collect the logs. I am trying to collect the logs on system crash. On system crash a soft reboot occurs without resetting the ram, i am reading the complete ram and organizing different sections. Best Regards, Sandeep

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RE: barrier()
by Pranay Kumar Srivastava Feb. 25, 2013

Feb. 25, 2013

> -----Original Message----- > From: kernelnewbies- > bounces%2Bpranay.shrivastava%3Dhcl.com(a)kernelnewbies.org > [mailto:kernelnewbies- > bounces%2Bpranay.shrivastava%3Dhcl.com(a)kernelnewbies.org] On Behalf Of > kernelnewbies-request(a)kernelnewbies.org > Sent: Monday, February 25, 2013 12:55 PM > To: kernelnewbies(a)kernelnewbies.org > Subject: Kernelnewbies Digest, Vol 27, Issue 52 > > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > or, via email, send a message with subject or body 'help' to > kernelnewbies-request(a)kernelnewbies.org > > You can reach the person managing the list at > kernelnewbies-owner(a)kernelnewbies.org > > When replying, please edit your Subject line so it is more specific than "Re: > Contents of Kernelnewbies digest..." > > > Today's Topics: > > 1. Re: atomic operations (Valdis.Kletnieks(a)vt.edu) > 2. valid address space ? (Abu Rasheda) > 3. Re: valid address space ? (Abu Rasheda) > 4. barrier() (Shraddha Kamat) > 5. Re: test jiffies on ARM SMP board (bill4carson) > 6. Re: test jiffies on ARM SMP board (bill4carson) > 7. Re: atomic operations (Kumar amit mehta) > 8. (Prasad Lakshman) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sun, 24 Feb 2013 18:24:21 -0500 > From: Valdis.Kletnieks(a)vt.edu > Subject: Re: atomic operations > To: richard -rw- weinberger <richard.weinberger(a)gmail.com> > Cc: Shraddha Kamat <sh2008ka(a)gmail.com>, kernelnewbies > <kernelnewbies(a)kernelnewbies.org> > Message-ID: <6017.1361748261(a)turing-police.cc.vt.edu> > Content-Type: text/plain; charset="us-ascii" > > On Sun, 24 Feb 2013 11:50:14 +0100, richard -rw- weinberger said: > > On Sun, Feb 24, 2013 at 10:42 AM, Shraddha Kamat <sh2008ka(a)gmail.com> > wrote: > > > what is the relation between atomic operations and memory alignment ? > > > > > > I read from UTLK that "an unaligned memory access is not atomic" > > > > > > please explain me , I am not able to get the relationship between > > > memory alignment and atomicity of the operation. > > > > Not all CPUs support unaligned memory access, such an access may cause > > a fault which needs to be fixed by the kernel... > > There's a more subtle issue - an unaligned access can be split across a cache > line boundary, requiring 2 separate memory accesses to do the read or write. > This can result in CPU A fetching the first half of the variable, CPU B updating > both halves, and then A fetching the second half of the now updated > variable.. This can bite you even on CPUs that support unaligned accesses. > >

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barrier()
by Shraddha Kamat Feb. 25, 2013

Feb. 25, 2013

#define barrier() asm volatile("" ::: "memory") What exactly volatile("" ::: "memory") doing here ? I was referring to gnu as (ver 2.14) manual but could not get much clue about this assembly construct - any pointers ?

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Re: atomic operations
by Peter Teoh Feb. 25, 2013

Feb. 25, 2013

Another good article on atomicty and data sizes: http://www.ibm.com/developerworks/library/pa-atom/ On Sun, Feb 24, 2013 at 8:50 PM, Peter Teoh <htmldeveloper(a)gmail.com> wrote: > in simple terms, any operation, in terms assembly instructions, which can > be executed in ONE instruction, is "atomic", because, just like an atom, it > cannot be broken up into parts. any instructions that is longer than one, > for eg, TWO instruction, is NOT atomic, because in BETWEEN the first and > 2nd instruction, something like an interrupt can come in, and affect the > values of the operand when it is passed from instruction one to second > instruction. To save me from reiteration: > > http://www.ibm.com/developerworks/library/pa-dalign/ (search for > "atomicity"). > > http://stackoverflow.com/questions/381244/purpose-of-memory-alignment > > http://lwn.net/Articles/260832/ > > http://www.songho.ca/misc/alignment/dataalign.html > > > http://www.cis.upenn.edu/~palsetia/cit595s08/Lectures08/alignmentOrdering.p… > > Essentially, atomicity and non-alignment become problematic when u tried > to to read using non-byte addressing mode with non-aligned address. > > On Sun, Feb 24, 2013 at 5:42 PM, Shraddha Kamat <sh2008ka(a)gmail.com>wrote: > >> what is the relation between atomic operations and memory alignment ? >> >> I read from UTLK that "an unaligned memory access is not atomic" >> >> please explain me , I am not able to get the relationship between >> memory alignment and atomicity of the operation. >> >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies(a)kernelnewbies.org >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> > > > > -- > Regards, > Peter Teoh > -- Regards, Peter Teoh

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Re: test jiffies on ARM SMP board
by bill4carson Feb. 25, 2013

Feb. 25, 2013

On 2013年02月21日 01:30, Russell King - ARM Linux wrote: > On Wed, Feb 20, 2013 at 10:54:41PM +0530, anish kumar wrote: >> On Thu, 2013-02-21 at 00:39 +0800, buyitian wrote: >>> i am confused about my test. in one device driver, >>> i put below code: >>> >>> printk("start to test test jiffies\n"); >>> >>> local_irq_save(flags); >>> >>> jf1 = jiffies; // read jiffies first time >>> >>> // hold cpu for about 2 seconds(do some calculation) >>> >>> jf2 = jiffies; // read jiffies after 2 seconds >>> >>> local_irq_restore(flags); >>> >>> printk("jf1:%lu, jf2:%lu\n", jf1, jf2); >>> >>> and the output is as below: >>> >>> <4>[ 108.551124]start to test test jiffies >>> <4>[ 110.367604]jf1:4294948151, jf2:4294948151 >>> >>> the jf1 and jf2 are the same value, although they are >>> read between 2 seconds interval, i think this is because >>> i disabled local interrupt. >>> but the printk timestamp is from 108.551124 to 110.367604, >>> which is about 2 seconds. and on my platform, printk timestamp >>> is got from the function read_sched_clock: >>> static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read; >>> >>> and function jiffy_sched_clock_read() is to read from jiffies. >>> >>> it seems that the jiffies is frozen when local irq is disabled, >>> but after local_irq_restore(), the jiffies not only start >>> to run, but also recover the lost 2 seconds. >>> >>> is the jiffies updated from another cpu when irq is disabled on >>> local cpu? >>> >>> is there some internel processor interrupt between cpu1 and cpu0 >>> after local irq is re-enabled so that jiffies recover the lost 2 seconds? >> I think it is because of the fact that some RTC registers keep the > > The RTC has nothing to do with this. > > As soon as the IRQs are allowed again (immediately after the > local_irq_restore()) the pending interrupt - including the timer > interrupt will be processed. > > At this point, because we read the clocksource, we can see that two > seconds have passed, and so we advance jiffies by the elapsed time. 80 /* 81 * Event handler for periodic ticks 82 */ 83 void tick_handle_periodic(struct clock_event_device *dev) 84 { 85 int cpu = smp_processor_id(); 86 ktime_t next; 87 88 tick_periodic(cpu); 89 90 if (dev->mode != CLOCK_EVT_MODE_ONESHOT) 91 return; 92 /* 93 * Setup the next period for devices, which do not have 94 * periodic mode: 95 */ 96 next = ktime_add(dev->next_event, tick_period); 97 for (;;) { 98 if (!clockevents_program_event(dev, next, ktime_get())) <--- once irq enabled, here we got -ETIME, then 99 return; 100 /* 101 * Have to be careful here. If we're in oneshot mode, 102 * before we call tick_periodic() in a loop, we need 103 * to be sure we're using a real hardware clocksource. 104 * Otherwise we could get trapped in an infinite 105 * loop, as the tick_periodic() increments jiffies, 106 * when then will increment time, posibly causing 107 * the loop to trigger again and again. 108 */ 109 if (timekeeping_valid_for_hres()) 110 tick_periodic(cpu); <---- here, we add missing jiffies 111 next = ktime_add(next, tick_period); 112 } 113 } > > This means printk() sees that the two seconds have passed. But because > you're reading from jiffies within the interrupt disabled region, that > code can't see the missed ticks. > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel(a)lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > -- 八百里秦川尘土飞扬,三千万老陕齐吼秦腔。 --bill

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