September 2014 - kernelnewbies@kernelnewbies.org

Why built-in modules slow down kernel boot?
by Michele Curti Sept. 30, 2014

Sept. 30, 2014

Hi all, it's just a curiosity. Since the use of an initramfs doubles the kernel boot time I decided to play a little compiling as built-in the modules required to mount root (starting from a localmodconfig). Everything ok, the system starts and the kernel boot time is good Startup finished in 1.749s (firmware) + 375ms (loader) + 1.402s (kernel) + 716ms (userspace) = 4.244s (from systemd-analyze). My next idea was: "Well, why not to make all modules as built-in? So I avoid reading from disk at every module load.. and all of them are loaded anyway", but the results was opposite to my expectations, kernel boot time increased from 1.4 to 3 seconds. So my question is, how this can be explained? My theory is that by compiling all the modules as built-in, the kernel calls all the module __init functions in a sequential manner, (using a single core?) and lets the userspace start only when everything is done. But I'm not sure at all. I have a samsung ativ book 9 liite: 1GHz 4core, ssd Regards, Michele

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Timing issues with RPi GPIO misc char driver
by mhornung.linux＠gmail.com Sept. 30, 2014

Sept. 30, 2014

Hello, I am trying to do my first driver, a Raspberry Pi misc char driver for controlling 433 MHz power plugs. The transmitter is a 433 MHz radio module connected to one of the RPi's GPIOs, the receiver is a 433 MHz power plug. The power plug expects a specific protocol which is normally send by an encoder chip (PT2260 or PT2262) within the appropriate remote control. The char driver shall replace those encoder chips and generate the correct bit sequence by the GPIO. I already have a user-space library [1] which works if I send the codeword multiple times (no real time kernel). Now I am trying to do this in kernel space which is where I ran into the same problem. The socket does only switch if I send the codeword multiple times (e.g. #define REPEAT 3). I would really appreciate any hint on how to get around this problem. Any comment on the code in general is also highly desirable. With best regards Michael [1] https://github.com/graznik/librsswitch <code> #include <linux/cdev.h> #include <linux/ctype.h> #include <linux/delay.h> #include <linux/device.h> #include <linux/fs.h> #include <linux/gpio.h> #include <linux/init.h> #include <linux/kdev_t.h> #include <linux/kernel.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/time.h> #include <linux/types.h> #include <linux/uaccess.h> #include <linux/moduleparam.h> #include <linux/miscdevice.h> #define GPIO4 4 /* The default GPIO pin */ #define REPEAT 1 /* Times to repeat the codeword */ #define HIGH 1 #define LOW 0 #define PULSE_LEN 350 /* * Each encoder chip used in the power socket remote controls can be described * with the following struct. */ struct Encoder { char **groups; /* Group identifiers */ uint ngroups; /* Number of groups */ char **sockets; /* Socket identifiers */ uint nsockets; /* Number of sockets within one group */ char **data; /* On or off */ uint ndata; /* On or off => 2 */ uint pulse_len; /* This might differ */ }; /* The 433 MHz sender must be connected to one of these pins */ static uint valid_gpios[] = {4, 17, 21, 22, 23, 24, 25}; static int send_pin = GPIO4; /* The default pin */ module_param(send_pin, int, 0644); MODULE_PARM_DESC(send_pin, "GPIO the 433 MHz sender is connected to"); static void transmit(int nhigh, int nlow) { /* * FIXME: PULSE_LEN is the pulse length in us. This should be a parameter in the future, depending on the encoder chip within the remote control. */ gpio_set_value(send_pin, HIGH); udelay(PULSE_LEN * nhigh); gpio_set_value(send_pin, LOW); udelay(PULSE_LEN * nlow); } /** * Sends a Tri-State "0" Bit * _ _ * Waveform: | |___| |___ */ static void send_0(void) { transmit(1, 3); transmit(1, 3); } /** * Sends a Tri-State "1" Bit * ___ ___ * Waveform: | |_| |_ */ static void send_1(void) { transmit(3, 1); transmit(3, 1); } /** * Sends a Tri-State "F" Bit * _ ___ * Waveform: | |___| |_ */ static void send_f(void) { transmit(1, 3); transmit(3, 1); } /** * Sends a "Sync" Bit * _ * Waveform Protocol 1: | |_______________________________ * _ * Waveform Protocol 2: | |__________ */ static void send_sync(void) { transmit(1, 31); } static void send_tris(char *codeword) { int i = 0; unsigned long flags; local_irq_save(flags); while (codeword[i] != '\0') { switch (codeword[i]) { case '0': send_0(); break; case '1': send_1(); break; case 'F': send_f(); break; } i++; } send_sync(); local_irq_restore(flags); } /** * Configure struct for the PT2260 encoder * @param pt2260 Pointer to a pt2260 instance */ static int pt2260_init(struct Encoder *pt2260) { char * const groups[] = {"1FFF", "F1FF", "FF1F", "FFF1"}; char * const sockets[] = {"1FF0", "F1F0", "FF10"}; char * const data[] = {"0001", "0010"}; int i; /* Four possible switch groups */ pt2260->ngroups = 4; pt2260->groups = kmalloc(pt2260->ngroups * sizeof(char *), GFP_KERNEL); if (pt2260->groups == NULL) { pr_err("modrss: Cannot kmalloc\n"); return -1; } /* Three possible switches per group */ pt2260->nsockets = 3; pt2260->sockets = kmalloc(pt2260->nsockets * sizeof(char *), GFP_KERNEL); if (pt2260->sockets == NULL) { pr_err("modrss: Cannot kmalloc\n"); return -1; } /* Data is either "On" or "Off" */ pt2260->ndata = 2; pt2260->data = kmalloc(pt2260->ndata * sizeof(char *), GFP_KERNEL); if (pt2260->data == NULL) { pr_err("modrss: Cannot kmalloc\n"); return -1; } for (i = 0; i < pt2260->ngroups; i++) pt2260->groups[i] = groups[i]; for (i = 0; i < pt2260->nsockets; i++) pt2260->sockets[i] = sockets[i]; for (i = 0; i < pt2260->ndata; i++) pt2260->data[i] = data[i]; return 0; } /** * Configure struct for the PT2262 encoder * @param *pt2262 Pointer to a pt2262 instance */ static int pt2262_init(struct Encoder *pt2262) { char * const groups[] = {"FFFF", "0FFF", "F0FF", "00FF", "FF0F", "0F0F", "F00F", "000F", "FFF0", "0FF0", "F0F0", "00F0", "FF00", "0F00", "F000", "0000"}; char * const sockets[] = {"F0FF", "FF0F", "FFF0", "FFFF"}; char * const data[] = {"FFF0", "FF0F"}; int i; /* 16 possible switch groups (A-P in Intertechno code) */ pt2262->ngroups = 16; pt2262->groups = kmalloc(pt2262->ngroups * sizeof(char *), GFP_KERNEL); if (pt2262->groups == NULL) { pr_err("modrss: Cannot kmalloc\n"); return -1; } /* Four possible switches per group */ pt2262->nsockets = 4; pt2262->sockets = kmalloc(pt2262->nsockets * sizeof(char *), GFP_KERNEL); if (pt2262->sockets == NULL) { pr_err("modrss: Cannot kmalloc\n"); return -1; } /* Data is either "On" or "Off" */ pt2262->ndata = 2; pt2262->data = kmalloc(pt2262->ndata * sizeof(char *), GFP_KERNEL); if (pt2262->data == NULL) { pr_err("modrss: Cannot kmalloc\n"); return -1; } for (i = 0; i < pt2262->ngroups; i++) pt2262->groups[i] = groups[i]; for (i = 0; i < pt2262->nsockets; i++) pt2262->sockets[i] = sockets[i]; for (i = 0; i < pt2262->ndata; i++) pt2262->data[i] = data[i]; return 0; } /** * Emulate an encoder chip * @param *enc Pointer to an encoder instance * @param uint group Socket group * @param uint socket Socket within group * @param uint data Data to send */ static int socket_ctrl(struct Encoder *enc, uint group, uint socket, uint data) { int i; size_t s; char *codeword; /* Calculate the codeword size */ s = strlen(enc->groups[group]) + strlen(enc->sockets[socket]) + strlen(enc->data[data]); codeword = kmalloc(s + 1, GFP_KERNEL); /* Generate the codeword including '\0' */ snprintf(codeword, s + 1, "%s%s%s", enc->groups[group], enc->sockets[socket], enc->data[data]); pr_debug("codeword: %s\n", codeword); /* Send the codeword */ for (i = 0; i < REPEAT; i++) send_tris(codeword); return 0; } static int socket_send(uint dev, uint group, uint socket, uint data) { struct Encoder encoder; switch (dev) { case 0: pt2260_init(&encoder); break; case 1: pt2262_init(&encoder); break; default: pr_err("modrss: Unknown encoder type.\n"); return -1; } socket_ctrl(&encoder, group, socket, data); return 0; } static ssize_t driver_write(struct file *f, const char __user *ubuf, size_t len, loff_t *off) { char *kbuf; uint encoder, group, socket, data; int i, data_len; kbuf = kmalloc(len, GFP_KERNEL); if (!kbuf) return -ENOMEM; if (copy_from_user(kbuf, ubuf, len)) { pr_err("Error: Unable to read user input\n"); kfree(kbuf); return -EFAULT; } data_len = strlen(kbuf); /* Check for valid hex values from user space */ for (i = 0; i < data_len; i++) { if ((kbuf[i] >= 'a') && (kbuf[i] <= 'f')) { kbuf[i] = kbuf[i] - 'a'; } else if ((kbuf[i] >= 'A') && (kbuf[i] <= 'F')) { kbuf[i] = kbuf[i] - 'A'; } else if ((kbuf[i] >= '0') && (kbuf[i] <= '9')) { kbuf[i] = kbuf[i] - '0'; } else { pr_err("modrss: Only characters 0-9, a-f, and A-F.\n"); return -1; } } pr_debug("modrss: socket_ctrl(%d, %d, %d, %d)\n", (uint)kbuf[0], (uint)kbuf[1], (uint)kbuf[2], (uint)kbuf[3]); socket_send((uint)kbuf[0], (uint)kbuf[1], (uint)kbuf[2], (uint)kbuf[3]); return len; } static const struct file_operations fops = { .owner = THIS_MODULE, .write = driver_write, }; static struct miscdevice modrss_dev = { .minor = MISC_DYNAMIC_MINOR, .name = "rsswitch", .fops = &fops, }; static int __init modrsswitch_init(void) { int ret, i, valid; pr_debug("modrss: Module registered"); misc_register(&modrss_dev); valid = 0; /* Check for valid GPIO */ for (i = 0; i < ARRAY_SIZE(valid_gpios); i++) { if (send_pin == valid_gpios[i]) { valid = 1; break; } } if (valid) { send_pin = GPIO4; pr_err("modrss: using default GPIO %d\n", GPIO4); } /* Register GPIO and set to LOW */ ret = gpio_request_one(send_pin, GPIOF_OUT_INIT_LOW, "send_pin"); if (ret) { pr_err("modrss: Unable to request GPIO: %d\n", ret); return ret; } pr_debug("modrss: Using GPIO %d\n", send_pin); return 0; } static void __exit modrsswitch_exit(void) { gpio_set_value(send_pin, 0); gpio_free(send_pin); misc_deregister(&modrss_dev); pr_debug("modrss: Module unregistered"); } module_init(modrsswitch_init); module_exit(modrsswitch_exit); MODULE_AUTHOR("Michael Hornung"); MODULE_DESCRIPTION("Remote socket switch character driver"); MODULE_LICENSE("GPL"); </code>

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Banned Again
by Nick Krause Sept. 29, 2014

Sept. 29, 2014

I am getting very annoyed , that I am banned again from my other email at yocto6(a)gmail.com are people trying to just prevent me from being on the list. Is that your goal now? Cheers Nick

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TODO: no enums in user space interface
by Gustavo A. R. Silva Sept. 29, 2014

Sept. 29, 2014

Hello everybody, There is a TODO file into drivers/staging that says the following: User space interface refinement: No enums should be used Can someone explain me what is the meaning of not using enums in user space interfaces? Thanks in advance Best regards -- Gustavo Silva <http://twitter.com/embeddedgus>

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On Page table walk.
by mind entropy Sept. 29, 2014

Sept. 29, 2014

Hi, I am experimenting with page table walking. I run a user space program and set the device attribute (of my sample device driver) in the sysfs. (DEVICE_ATTR) which is the address of the variable in the user space. I get the current->mm to get the current task memory descriptor and use it to walk the pages. Once I get the pte address I reboot and dump the memory at that point using u-boot. (md.b <addr> 1) but I do not find the value present there. Sample code: (This is just for illustration and experimenting and does not contain error checks etc.). -------------------------------------------------------------------------------------------- ssize_t process_mem_test_attr_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) { struct task_struct *current_task; unsigned long addr_res; struct vm_area_struct *vmarea_struct_addr; pgd_t *pgd; pmd_t *pmd; pud_t *pud; pte_t *ptep, pte; struct page *page; int kval; int uval; DEFINE_SPINLOCK(test_lock); spin_lock_irq(&test_lock); current_task = current; if(current_task != NULL) { printk(KERN_ALERT "\nCurrent task pid: %d\n", current_task->pid); printk(KERN_ALERT "mm: 0x%lx, active_mm 0x%lx\n", current_task->mm,current_task->active_mm); printk(KERN_ALERT "Page global directory : 0x%lx\n", current_task->mm->pgd); printk(KERN_ALERT "mmap base : 0x%lx", current_task->mm->mmap_base); vmarea_struct_addr = current_task->mm->mmap; while(vmarea_struct_addr != NULL) { printk(KERN_ALERT "vm_start : 0x%lx, vm_end : 0x%lx\n", vmarea_struct_addr->vm_start, vmarea_struct_addr->vm_end); vmarea_struct_addr = vmarea_struct_addr->vm_next; } } else { printk(KERN_ALERT "Current task NULL\n"); } if(kstrtol(buf,10,&addr_res) != 0) { printk(KERN_ALERT "Error converting to long\n"); return count; } copy_from_user(&kval,(unsigned int *)addr_res,4); printk(KERN_ALERT "kval : %x\n",kval); printk(KERN_ALERT "addr: %lx\n",addr_res); pgd = pgd_offset(current_task->mm,addr_res); if(pgd_none(*pgd) || pgd_bad(*pgd)) { printk(KERN_ALERT "pgd bad\n"); return count; } else { printk(KERN_ALERT "pgd 0x%lx\n",pgd); } pud = pud_offset(pgd,addr_res); if(pud_none(*pud) || pud_bad(*pud)) { printk(KERN_ALERT "pud bad\n"); return count; } else { printk(KERN_ALERT "pud 0x%lx\n",pud); } pmd = pmd_offset(pud,addr_res); if(pmd_none(*pmd) || pmd_bad(*pmd)) { printk(KERN_ALERT "pmd bad\n"); return count; } else { printk(KERN_ALERT "pmd 0x%lx\n",pmd); } ptep = pte_offset_map(pmd,addr_res); if(!ptep) { printk(KERN_ALERT "ptep bad\n"); } else { printk(KERN_ALERT "ptep 0x%lx\n",ptep); } pte = *ptep; if(pte_present(pte)) { printk(KERN_ALERT "pte : 0x%lx\n",pte); page = pte_page(pte); } else { printk(KERN_ALERT "pte not present\n"); } printk(KERN_ALERT "pte with offset 0x%lx offset : 0x%lx\n", pte+((addr_res) & ((1<<PAGE_SHIFT)-1)), addr_res & ((1<<PAGE_SHIFT)-1)); while(1) ; printk(KERN_ALERT "After lock\n"); //Should not print this. return count; } -------------------------------------------------------------------------------------------- I use a spinlock to prevent the process from getting swapped. I disable the irq and make it spin on while(1); after which I reboot. After doing a memoy dump I find the value in the address but at an offset from pte value printed. What seems to be wrong with my approach? Thanks in advance.

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On virt_to_phys doubts.
by mind entropy Sept. 29, 2014

Sept. 29, 2014

Hi, I want to know the physical address [just for debugging and info.Not for DMA etc] of a particular virtual address allocated via kmalloc. I am running the below code on S3C2440 with 64MB of RAM. The /proc/meminfo returns MemTotal: 59164 kB MemFree: 35884 kB MemAvailable: 47148 kB I run the following module for printing the addresses. [This module is only for test. So excuse if I have cut corners]. ------------------------------------------------ #include <linux/init.h> #include <linux/kernel.h> #include <linux/printk.h> #include <linux/module.h> #include <linux/gfp.h> #include <linux/types.h> #include <linux/mm.h> #include <linux/mm_types.h> #include <linux/slab.h> static int vm_mem_test_init(void) { void *km; printk(KERN_ALERT "vm mem test init\n"); km = kmalloc(1,GFP_KERNEL); if(km == NULL) { printk(KERN_ALERT "Could not kmalloc\n"); return -1; } else { printk(KERN_ALERT "Allocated\n"); printk(KERN_ALERT "Virtual addr : %x\n",(unsigned int)km); printk(KERN_ALERT "Kernel physical addr : 0x%x\n",virt_to_phys(km)); kfree(km); } return 0; } The output for the following is: Virtual addr : c2c080e0 Kernel physical addr : 0x32c080e0 ----------------------------------------------------------- The kernel physical address is wrong as I only have 64MB. Should I be doing a kernel page table walk to get the associated physical address? Thanks Gautam.

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Query regarding memory accesses and page faults in virtual machine using kvm and qemu
by ravali pullela Sept. 29, 2014

Sept. 29, 2014

Hello everyone, I am using kvm and VM OS is ubuntu 14.04. Host hardware is intel core i5, running ubuntu 14.04 OS. Background:I am trying to track the number of pages accessed by a VM in certain period of time. To do this, I am setting the pte flags of all pages present and which are not protected (i.e., PROTNONE != 1) on the host virtual address space belonging to the VM process as NOT PRESENT AND PROTECTED (by clearing PRESENT bit and setting PROTNONE bit in the pte entry). That is, for pages belonging to the VM process, if they are present and not protected, mark their pte entries to reflect that they are not present but protected. The idea is that whenever this page is accessed, there has to be a fault because the present bit is cleared. Now, inside the fault handler handle_pte_fault, I registered a kernel module function, which will reset the pte bits for the faulted address. [Resetting means making PRESENT = 1 and PROTNONE = 0] I am considering the VM as any other normal process on the host. Current Scenario:I am testing the above by running a sample test program inside the VM which does the following. 1) Mallocs 200 MB which is 51200 pages. 2) Accesses all the pages to make sure that they are brought into memory. 3) sleep for say 10 secs to allow tracker to mark the pages 4) access all the pages [which is expected to generate faults] Ran this test process couple of times. My tracker is runs on host. Issue: My tracker module reports very few pages as accessed which is in turn because of very few faults say around 350 faults for 51200 which are expected. Also I am doing a tlb_flush_all in host to avoid direct translations after the pages are marked and before they are accessed. Note: I disabled ksm and huge pages features. I tested the tracker on a process running on the host which malloced 900 MB and accesses all the pages, and it reflects the pages dirtied as the number of pages dirtied. But the issue happens only in the case of tracking VMs. Queries:1) Are all the tlb entries flushed when tlb_flush_all is done or are the tlb entries of VM tagged separately and this is causing an issue? 2) Can anyone please guide as to what could be going wrong? Or any comments on the procedure that could go wrong would help. Any references would also help as I am new to this qemu, kvm memory management area. Thanks, Ravali

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Query on IIO consumer driver and device tree
by sanchayan maity Sept. 29, 2014

Sept. 29, 2014

Hello, There is an ADC driver following the IIO framework. I am using Kernel 3.17 rc5 in an embedded device. I am in the process of writing a "consumer" IIO touchscreen driver which uses the ADC channels. http://lxr.free-electrons.com/source/Documentation/devicetree/bindings/iio/… I am following this document and my device tree node is as follows for the touchscreen driver. vf_touchctrl { compatible = "vf-touch"; io-channels = "&adc0 0", &adc0 1", "&adc1 0", "&adc1 2"; pinctrl-names = "idle", "default"; pinctrl-0 = "&pinctrl_default"; pinctrl-1 = "&pinctrl_idle"; gpio-xp = "&gpio0 8 0" .... /* Few more gpio entries like this */ }; In the touchscreen driver, i will be using the IIO consumer functions from http://lxr.free-electrons.com/source/include/linux/iio/consumer.h. When i call iio_channel_get_all(), i am expecting to get pointers to the four channels in order specified in the DT above. Is my understanding correct? Then specify these four channel pointers with iio_read_channel_raw() to get the ADC readings. My other question is related to the GPIO entry in the DT above. When using of_get_named_gpio(), i do it like below. int ret = of_get_named_gpio(node, "gpio-xp", 0); I do not get the correct values, but negative error values. Also, i can see a "argument longer than property" error for the device tree parsing in dmesg log. Can someone point out what i am doing wrong here? Thanks & Regards, Victor aka Sanchayan.

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Doubt in USB Drivers
by me storage Sept. 28, 2014

Sept. 28, 2014

Hi to all I am new to Linux Kernel Programming .I want to develop usb drivers so i read LDD3 Chapter 14. i didn't find /sbin/hotplug in Ubuntu 12.04.And my doubt is how kernel handles the usb devices i.e who detects usb events ,then who fires hotplug script to run ,where kernel searches corresponding module ,who loads the modules etc... Any resources are helpful to me Thanks to all

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Re: Doubt in USB Drivers
by me storage Sept. 28, 2014

Sept. 28, 2014

Yes it is a task in Eudyptula Challenge, I read the chapter which little mentioned ,after searching on google i found some solutions but i don't want to copy those solutions i want to solve my self .So that's why i asked for resources not any solution ? Please try to understand . Thanks to all On 28 September 2014 19:27, Sudip Mukherjee <sudipm.mukherjee(a)gmail.com> wrote: > > On Sep 28, 2014 4:28 PM, "me storage" <me.storage126(a)gmail.com> wrote: > > > > Hi to all > > I am new to Linux Kernel Programming .I want to develop usb drivers so i > read LDD3 Chapter 14. i didn't find /sbin/hotplug in Ubuntu 12.04.And my > doubt is how kernel handles the usb devices i.e who detects usb events > ,then who fires hotplug script to run ,where kernel searches corresponding > module ,who loads the modules etc... > > is it related to the task of Eudyptula Challenge?? > > looks like .... > > > Any resources are helpful to me > > Thanks to all > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies(a)kernelnewbies.org > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > >

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