January 2017 - kernelnewbies@kernelnewbies.org

How to propose a patch to the kernel mainline
by Abel Jan. 27, 2017

Jan. 27, 2017

Hi! First, I apologize as I guess this topic has been treated many times here. I'm already coding for a patch intended to be merged with the kernel mainline. It adds a small new feature, so it's not a little bug fix, but still not so big deal. I'll get it compiling and working before I submit the patch to the mailing list, that's clear to me; but I'm sure there will be mistakes, stuff I didn't think/know about, some styling issues and, maybe, a technical discussion of how it should be done. *What I want to ask it's what are the best steps I should walk through in order to get this patch merged.* I've already done some modifications of the Linux kernel for university works, I've also contributed to other open source projects. But I've never tried to contribute to code to the upstream kernel code before. *Greetings,* * Akronix.*

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File Descriptor allocation
by vish chopra Jan. 26, 2017

Jan. 26, 2017

Hi, i would like to know how a fd is allocated to a process? Flow chat of function calling, i.e which function are called during allocation of fd to a process. please help with this. Thanx in advance Regards, Vishal Chopra +91-7837583269

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custom audio card on beaglebone
by jo Jan. 25, 2017

Jan. 25, 2017

Hi everyone, I am currently trying to get a simple audio I2S DAC board (https://polyvection.com/shop/plaindac/) to work on a beaglebone green wireless. The components is a PCM5121, a popular one that has an existing driver. so far, - I have a custom compiled kernel with the apropriate driver compiled $ grep PCM512 .config CONFIG_SND_SOC_PCM512x=m CONFIG_SND_SOC_PCM512x_I2C=m - I can boot with a custom device tree including my definition of the board as an "asoc-simple-card" and it get recognise without error on boot. root@beaglebone:~# dmesg |grep sound [ 28.730678] asoc-simple-card sound: pcm512x-hifi <-> 48038000.mcasp mapping ok root@beaglebone:~# lsmod |grep pcm512 snd_soc_pcm512x_i2c 2782 1 snd_soc_pcm512x 24341 1 snd_soc_pcm512x_i2c snd_soc_core 192029 5 snd_soc_pcm512x,snd_soc_davinci_mcasp,snd_soc_edma,snd_soc_omap,snd_soc_simple_card snd_pcm 103172 6 snd_soc_pcm512x,snd_soc_davinci_mcasp,snd_soc_core,snd_soc_omap,snd_pcm_dmaengine - I can open the device with alsamixer, and can confirm the sound is on 100% Howewer, I still can't get any sound of the device. Does someone has experience in regards to asoc audio device and cant give me some thought on easy to miss things ? I am still trying to figure out if I have omitted something on the device tree, or if I need to configure something more on the OS (alsa, pulseaudio ?)... I have attached my device tree, if someone feel like giving a look at it. (my addition from the original one comes after line 73). Also some output that may give you more info that they are giving to me: root@beaglebone:~# aplay -v Pom\ Pom.wav Playing WAVE 'Pom Pom.wav' : Signed 32 bit Little Endian, Rate 44100 Hz, Stereo ALSA <-> PulseAudio PCM I/O Plugin Its setup is: stream : PLAYBACK access : RW_INTERLEAVED format : S32_LE subformat : STD channels : 2 rate : 44100 exact rate : 44100 (44100/1) msbits : 32 buffer_size : 22050 period_size : 5512 period_time : 125000 tstamp_mode : NONE period_step : 1 avail_min : 5512 period_event : 0 start_threshold : 22050 stop_threshold : 22050 silence_threshold: 0 silence_size : 0 boundary : 1445068800 #nothing play and the above stay displayed -as is- until I ctrl-c root@beaglebone:~# aplay -l **** List of PLAYBACK Hardware Devices **** card 0: plaindac [plaindac], device 0: davinci-mcasp.0-pcm512x-hifi pcm512x-hifi-0 [] Subdevices: 0/1 Subdevice #0: subdevice #0 root@beaglebone:~# cat /proc/asound/card0/pcm0p/info card: 0 device: 0 subdevice: 0 stream: PLAYBACK id: davinci-mcasp.0-pcm512x-hifi pcm512x-hifi-0on name: subname: subdevice #0 class: 0 subclass: 0 subdevices_count: 1 subdevices_avail: 0 Regards, Jonathan.

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Help on modelling gpio interrupt source when interrupt is shared
by Rajasekhar Pulluru Jan. 24, 2017

Jan. 24, 2017

Hi, I have a query on device tree pertaining to modelling a gpio pin as an interrupt source. I have searched mailing list archives and kernel documentation before posting this and couldn't get any direct solution. (My understanding is limited and hence posting the query below:) My SOC has a gpio controller and uart both sharing same interrupt line as specified below. interrupt-parent = <&gic>; mygpio: gpio@0x19008000 { compatible = "mysoc,mygpio-controller,gc"; #address-cells = <1>; #size-cells = <1>; #gpio-cells = <2>; reg = gpio: <0x19008000 0x50>; ngpios = <12>; pin-offset = <4>; pin-base = <4>; irq-base = <256>; /* sw irq base for irq handlers */ gpio-controller; interrupt-controller; interrupts = <GIC_SPI 91 IRQ_TYPE_LEVEL_HIGH>; }; uart0: serial@0x19000300 { compatible = "snps,dw-apb-uart"; reg = <0x19000300 0x100>; interrupts = <GIC_SPI 91 IRQ_TYPE_LEVEL_HIGH>; clock-frequency = <62500000>; }; gpio pin 0 of mygpio is used as an interrupt source for detecting the presence of external pluggable device (that is not driven by kernel). And I intend to detect the presence of the pluggable device from user space by means of generic uio platform driver using below device tree configuration. (following https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt/) user_io@0 { compatible = "mydevice,generic-uio,ui_pdrv"; status = "okay"; interrupt-parent = <&mygpio>; interrupts = <0 IRQ_TYPE_LEVEL_HIGH>; }; Running modprobe uio_pdrv_genirq of_id="mydevice,generic-uio,ui_pdrv" and creating /dev/uio0 using mknod (major number from cat /proc/devices | grep uio), I couldn't see an irq entry bind to uio driver under /proc/interrupts. Am I doing anything wrong here? Other method I have tried to get notified of the gpio pin0 interrupt in user space is to poll on /sys/class/gpio/gpio0/value. But merely exporting gpio0 wasn't sufficient as kernel should make a call to request_irq on the gpio0 interrupt line. Is there a generic driver framework (like pinctrl) that can export a device node to register the gpio pin0 as an interrupt source that allows me to poll on its sysfs entry? Thanks, Rajasekhar

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Bad block Management Patch
by Anurag Raghavan (RBEI/ETW11) Jan. 24, 2017

Jan. 24, 2017

Hi All, I am using kernel version-3.0.35 I am facing uncorrectable ECC error in ubifs. I am suspecting, it is because of bad blocks are not properly handled in my driver. Is there any patches available to handle the bad block in the specified version... Best regards Raghavan Anurag RBEI/ETW1 Tel. +91(422)667-4001 | Mobil 9986968950

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more questions about UAPI content -- why some usages of "__KERNEL__"?
by Robert P. J. Day Jan. 23, 2017

Jan. 23, 2017

a couple more questions about UAPI in the kernel source, just to clarify that there is still some cleanup that could be done. first, i get that whole idea behind the include/uapi/ directory ... that it's way cleaner to factor out the userspace content to a single location, and use that as the basis for a subsequent "kernel-headers" package or something to that effect. but even having done that, there is of course some necessary usage of testing the __KERNEL__ macro to see if one is preprocessing in kernel space or not. one of these uses is, say, in a uapi header file, there might be a test to include a structure member depending on whether you're in kernel space or user space. but consider the following example. here's include/linux/mtd/inftl.h, wherein an entire chunk of that header file is protected by a "__KERNEL__" test: #ifndef __MTD_INFTL_H__ #define __MTD_INFTL_H__ ... snip ... #ifdef __KERNEL__ <--- start test struct INFTLrecord { struct mtd_blktrans_dev mbd; __u16 MediaUnit; __u32 EraseSize; struct INFTLMediaHeader MediaHdr; int usecount; unsigned char heads; unsigned char sectors; unsigned short cylinders; __u16 numvunits; __u16 firstEUN; __u16 lastEUN; __u16 numfreeEUNs; __u16 LastFreeEUN; /* To speed up finding a free EUN */ int head,sect,cyl; __u16 *PUtable; /* Physical Unit Table */ __u16 *VUtable; /* Virtual Unit Table */ unsigned int nb_blocks; /* number of physical blocks */ unsigned int nb_boot_blocks; /* number of blocks used by the bios */ struct erase_info instr; }; int INFTL_mount(struct INFTLrecord *s); int INFTL_formatblock(struct INFTLrecord *s, int block); void INFTL_dumptables(struct INFTLrecord *s); void INFTL_dumpVUchains(struct INFTLrecord *s); int inftl_read_oob(struct mtd_info *mtd, loff_t offs, size_t len, size_t *retlen, uint8_t *buf); int inftl_write_oob(struct mtd_info *mtd, loff_t offs, size_t len, size_t *retlen, uint8_t *buf); #endif /* __KERNEL__ */ <--- end test #endif /* __MTD_INFTL_H__ */ is that test really necessary? this is a header file that should be included *only* from within kernel space -- how could it possibly end up being used from user space? or am i missing something? i can see the value in uapi header files still needing to test __KERNEL__, in case there are minor tweaks to be done. but it seems that there should be precious little need for testing __KERNEL__ in *kernel* header files once userspace content has been factored out and moved to uapi, no? thoughts? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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initrd and messages in the kernel log
by Kevin Wilson Jan. 20, 2017

Jan. 20, 2017

Hello, Question: in the boot process on my machine (Ubuntu 14), the standard Ubuntu initrd image is used. In that process of bootstrapping from initrd, several kernel modules from the initrd module are used. I believe that some of these modules are printing module messages using the standard kernel mechanism. Question in: from what I see, these messages do not appear in the kernel log (/var/log/syslog). Is there a way to enable getting these messages to the kernel log ? Kevin

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skb_find_text()
by Jannik Becher Jan. 20, 2017

Jan. 20, 2017

Hi there, I have a problem with the function skb_find_text(). Commit 059a2440fd3cf4ec57735db2c0a90401cde84fca removes the state argument from the parameters with the hint, that it isn't needed by the caller. But is it not needed by the function textsearch_next? Example: int pos; struct ts_state state; for (pos = skb_find_text(skb, 0, INT_MAX, conf); pos != UINT_MAX; pos = textsearch_next(conf, &state)) pr_info("String was found."); Is this the right way to search for a string? Thanks, Jannik Becher

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wake_up & wait_event are counting events ?
by Ran Shalit Jan. 19, 2017

Jan. 19, 2017

Hello, I am trying to correctly register interrupt in kernel for user interface: irq handler ========= static irqreturn_t irq_handler(int irq, void *dev_id) { struct elbit_irq_dev *elbit_irq = &elbit_irq_devices[0]; printk("irq in\n"); <<==== clear interrupt in fpga here or after the call to wake_up, (at the bottom of routine below ) ? atomic_set(&elbit_irq->flag, 1); wake_up_interruptible(&elbit_irq->pollw); return IRQ_HANDLED; } ioctl for waiting on interrupts ====================== static long elbit_device_ioctl( struct file *filp, /* ditto */ unsigned int ioctl_num, /* number and param for ioctl */ unsigned long ioctl_param) { struct elbit_irq_dev *elbit_irq = &elbit_irq_devices[0]; switch (ioctl_num) { case IOCTL_WAIT_IRQ: atomic_set(&elbit_irq->flag, 0); wait_event_interruptible(elbit_irq->pollw, atomic_read(&elbit_irq->flag) != 0) ; break; default: break; } return 0; } my questions: 1. does wake_up and wait_event are countable, i.e. if there are 2 interrupts for example before wait_event is called, does it mean it wake_event will not sleep on 2 consecutive calls ? 2. should we put the clear of interrupts in fpga in the interrupt before or after the wake_up ? can we put them instead in the userspace handler (IOCTL_WAIT_IRQ) instead of clearing the interrupt in the interrupt handler ? Thank you, Ran

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Downgrade GSM/UMTS module to USB 2.0 Fullspeed
by Oliver Graute Jan. 19, 2017

Jan. 19, 2017

Hello list, i'am using a GSM/UMTS Module on a PCB which is connected with USB 2.0 Hi-Speed to my imx6ul CPU. To reduce our Electromagnetic compatibility and to make my hardware colleges happy again I want to downgrade to USB Full Speed. How can I tell the Linux Kernel to Do so? I already tried this and looked around in /sys/bus/usb/devices but can't find appropirate place to force it to lower speed. dmesg | grep USB [ 175.775175] usb 1-1: new high-speed USB device number 2 using ci_hdrc [ 175.938753] usb 1-1: New USB device found, idVendor=1e2d, idProduct=005a [ 175.938797] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0 [ 176.021420] cdc_acm 1-1:1.0: ttyACM0: USB ACM device [ 176.068150] cdc_acm 1-1:1.2: ttyACM1: USB ACM device [ 176.102410] cdc_acm 1-1:1.4: ttyACM2: USB ACM device [ 176.131074] cdc_acm 1-1:1.6: ttyACM3: USB ACM device [ 176.172841] cdc_acm 1-1:1.11: ttyACM4: USB ACM device [ 176.208768] cdc_acm 1-1:1.13: ttyACM5: USB ACM device /sys/bus/usb/devices# lsusb -t /: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ci_hdrc/1p, 480M |__ Port 1: Dev 2, If 0, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 1, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 2, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 3, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 4, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 5, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 6, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 7, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 8, Class=, Driver=, 480M |__ Port 1: Dev 2, If 9, Class=, Driver=, 480M |__ Port 1: Dev 2, If 10, Class=, Driver=, 480M |__ Port 1: Dev 2, If 11, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 12, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 13, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 14, Class=, Driver=cdc_acm, 480M |__ Port 1: Dev 2, If 15, Class=, Driver=, 480M Best Regards, Oliver

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