June 2018 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Add IIO example to the kernelnewbies wiki
by Gaston Gonzalez Feb. 21, 2019

Feb. 21, 2019

Hi, I'm testing an AD7746 eval board using a Diolan DLN-2 adapter. I wrote some basic notes about the installation an instanciation process for my own use. But then I thought it could be useful for someone else. So maybe I could put this in the kernel newbies page under the IIO section? If you think is worth it, I would be glad to add it to the wiki page. Best regards, Gaston Notes: The setup ========= AD7746-EVAL BOARD --> Diolan DLN-2 Adapter --> Thinkpad T430 The connection between the AD7746 eval board and adapter is as detailed in [2] I2C Interface Configuration Options, External connection (pag 4). The connection between Diolan DLN-2 and the T430 is USB straighforward. Drivers ======= Both in mainline kernel: - Diolan DLN-2 driver: I2C_DLN2 (prompt Diolan DLN-2 USB I2C adapter) Loc: drivers/i2c/busses/ - AD7746: AD7746 Loc: drivers/staging/iio/cdc/ Bus of interest =============== $ sudo i2cdetect -l We get something like: ... i2c-10 i2c dln2-i2c-1-1.2:1.0-0 I2C adapter ... So our bus is the number 10. Getting the address =================== $ sudo i2cdetect -y -r 10 We get something like: 0 1 2 3 4 5 6 7 8 9 a b c d e f 00: -- -- -- -- -- -- -- -- -- -- -- -- -- 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 40: -- -- -- -- -- -- -- -- 48 -- -- -- -- -- -- -- 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 70: -- -- -- -- -- -- -- -- 3. Device instantiation: # echo add7746 0x48 > /sys/bus/i2c/devices/i2c-10/new_device We must see something like: $ cd /sys/bus/i2c/devices/i2c-10/10-0048/ $ ls driver iio:device0 modalias name power subsystem uevent $ cd iio:device0 $ ls dev in_capacitance-capacitance_calibbias in_capacitance0_calibbias_calibration in_capacitance-capacitance_sampling_frequency in_capacitance0_calibscale in_capacitance-capacitance_scale in_capacitance0_calibscale_calibration in_capacitance_sampling_frequency in_capacitance0-capacitance2_calibscale in_capacitance_sampling_frequency_available in_capacitance0-capacitance2_offset in_capacitance_scale in_capacitance0-capacitance2_raw in_temp0_input in_capacitance0_offset in_temp1_input in_capacitance0_raw in_voltage0_calibscale_calibration in_capacitance1_calibbias_calibration in_voltage0_raw in_capacitance1_calibscale in_voltage1_supply_raw in_capacitance1_calibscale_calibration in_voltage_sampling_frequency in_capacitance1-capacitance3_calibscale in_voltage_sampling_frequency_available in_capacitance1-capacitance3_offset in_voltage_scale in_capacitance1-capacitance3_raw name in_capacitance1_offset power in_capacitance1_raw subsystem in_capacitance_calibbias uevent Checking the permits: $ ll -r--r--r-- 1 root root 4096 mar 31 09:57 dev --w------- 1 root root 4096 mar 31 09:57 in_capacitance0_calibbias_calibration -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0_calibscale --w------- 1 root root 4096 mar 31 09:57 in_capacitance0_calibscale_calibration -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0-capacitance2_calibscale -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0-capacitance2_offset -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0-capacitance2_raw -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0_offset -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance0_raw --w------- 1 root root 4096 mar 31 09:57 in_capacitance1_calibbias_calibration -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1_calibscale --w------- 1 root root 4096 mar 31 09:57 in_capacitance1_calibscale_calibration -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1-capacitance3_calibscale -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1-capacitance3_offset -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1-capacitance3_raw -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1_offset -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance1_raw -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance_calibbias -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance-capacitance_calibbias -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance-capacitance_sampling_frequency -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance-capacitance_scale -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance_sampling_frequency -r--r--r-- 1 root root 4096 mar 31 09:57 in_capacitance_sampling_frequency_available -rw-r--r-- 1 root root 4096 mar 31 09:57 in_capacitance_scale -rw-r--r-- 1 root root 4096 mar 31 09:57 in_temp0_input -rw-r--r-- 1 root root 4096 mar 31 09:57 in_temp1_input --w------- 1 root root 4096 mar 31 09:57 in_voltage0_calibscale_calibration -rw-r--r-- 1 root root 4096 mar 31 09:57 in_voltage0_raw -rw-r--r-- 1 root root 4096 mar 31 09:57 in_voltage1_supply_raw -rw-r--r-- 1 root root 4096 mar 31 09:57 in_voltage_sampling_frequency -r--r--r-- 1 root root 4096 mar 31 09:57 in_voltage_sampling_frequency_available -rw-r--r-- 1 root root 4096 mar 31 09:57 in_voltage_scale -r--r--r-- 1 root root 4096 mar 31 09:57 name drwxr-xr-x 2 root root 0 mar 31 09:57 power lrwxrwxrwx 1 root root 0 mar 31 09:57 subsystem -> ../../../../../../../../../../../bus/iio -rw-r--r-- 1 root root 4096 mar 31 09:57 uevent 4. Capacitance According to [2], the capacitive length sensor is connected to CIN2+ and CIN2-. In the driver, the values are mapped to capacitance0. Raw values vs sensor length: Note: (+) values means the sensor was moved to the left, (-) values means the sensor was moved to the right. I.e. +1 cm means the rule was moved 1 to the left, while -1 means the rule was moved 1 cm to the right. Note2: note the raw value for -10 is 8224733, while +10 is -8224726, the difference is because when the rule is moved 10 cm to the left, the is still 2 o 3 cm of dielectric between the plates. The design is obviously thought to move the rule to the right. Length (cm) | Raw Value Cap0 ------------------------------ -10 -8224733 -9 -8224730 -8 -8224728 -7 -8224725 -6 -8224724 -5 -8224722 -4 -8224720 -3 -8224718 -2 -8224716 -1 -8224714 +0 -8224711 +1 -8224711 +2 -8224711 +3 -8224711 +4 -8224713 +5 -8224715 +6 -8224717 +7 -8224719 +8 -8224721 +9 -8224723 +10 -8224726 References ========== [1] http://www.analog.com/media/en/technical-documentation/data-sheets/AD7745_7… [2] http://www.analog.com/media/en/technical-documentation/evaluation-documenta… [3] https://i2c.wiki.kernel.org/index.php/Main_Page [4] https://kernelsense.wordpress.com/2016/01/22/achievement-unlocked-first-iio…

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Should I specify the mount type every time? What are the recommendations...?
by Julio Faracco June 28, 2018

June 28, 2018

Hi guys, I want your opinion about a syscall: mount(). Today, a problem brought back this doubt. I see a lots of code that calls/uses mount() syscall. But, recently, running Valgrind, it showed an error saying that you cannot specify NULL as the 'type' argument of mount function. An example from kernel code: ret = mount("/dev/pts/ptmx", "/dev/ptmx", NULL, MS_BIND, NULL); Valgrind was complaining about the first NULL parameter which refers to the mount type: ==18012== Syscall param mount(type) points to unaddressable byte(s) After replacing NULL to type "none" the error disappeared. I read a documentation about it, saying that is better to use "none" for BIND and MOVE options. But, I'm not right about that. Do you have any documentation or a best practice to use this syscall? Thanks! -- Julio Cesar Faracco

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clk: timestamps
by Subhashini Rao Beerisetty June 27, 2018

June 27, 2018

Hi All, In the kernel code I see it supports CLOCK_REALTIME \ CLOCK_MONOTONIC \ CLOCK_MONOTONIC_RAW timestamps. Can someone explain what’s major difference between those three modes and when to use which one? I’ve N number of Linux machines in the network with the same software running. Basically I need to collect the timestamps in kernel mode in all the machines and then compare, which(either CLOCK_REALTIME or CLOCK_MONOTIC_RAW or MONOTONIC) one would be the correct way? Thanks,

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staging: rtl8192u: Header file organisation and cleanup?
by John Whitmore June 27, 2018

June 27, 2018

Hello all, I've had a few goes at code style clean up of the file drivers/staging/rtl8192u/ieee80211/rtl819x_HTProc.c Unfortunately the low hanging fruit has been cleared, and a lot of the checkpatch errors are down to line length or to CamelCase. So I decided I'd have a look at camel case. I had a look at a local variable in the first function in the file: void HTUpdateDefaultSetting(struct ieee80211_device *ieee) { PRT_HIGH_THROUGHPUT pHTInfo = ieee->pHTInfo; Now that type PRT_HIGH_THROUGHPUT is declared in the header file #include "rtl819x_HT.h" which is included at the top of the C file. As is another header file: #include "ieee80211.h" These header files are the reason for this question. The ieee80211.h file also includes the rtl819x_HT.h file so the file is included twice, but protected by a #ifndef at the top of the file. So my first question would be if you were trimming the number of includes of that header file would the include in the C File be removed, or alternatively the include in ieee80211.h be removed? The second question is to do with the name of those files. I'm wroking in staging/rtl8192u but that header file name is mirrored in staging/rtl8192e $ find -name rtl819x_HT.h -print ./drivers/staging/rtl8192u/ieee80211/rtl819x_HT.h ./drivers/staging/rtl8192e/rtl819x_HT.h $ find . -name "*.[ch]" -exec grep "rtl819x_HT.h" {} /dev/null \; ./drivers/staging/rtl8192u/ieee80211/rtl819x_HTProc.c:#include "rtl819x_HT.h" ./drivers/staging/rtl8192u/ieee80211/ieee80211.h:#include "rtl819x_HT.h" ./drivers/staging/rtl8192e/rtl819x_HTProc.c:#include "rtl819x_HT.h" ./drivers/staging/rtl8192e/rtllib.h:#include "rtl819x_HT.h" I'm wondering given that there are two different files they should be renamed to rtl819u_HT.h and rtl819e_HT.h?

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Linux Networking Internals Question
by V.Ravikumar June 25, 2018

June 25, 2018

Hi All, I wanted to know how a packet received will be handovered to a correct user process. Basically I want to understand what are the various header parameters in packet which will help to find the open socket descriptor of respective user process. I'm not able to find the exact answers in the web. Thanks in advance Regards, Ravi

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audio samples data flow from user mode to kernel mode
by Subhashini Rao Beerisetty June 25, 2018

June 25, 2018

Hello All, I’m trying to understand how audio samples transferred between user mode to kernel mode during playback and capture. I’m using aplay & arecord alsa utilities for playback and capture. Let us take a PCM wav file of sample rate 48000 and it has a total number of samples 480000 (Approx.Duration in seconds=10). Size of each sample is 8 bytes(two channels). After invocation of aplay from user mode, how does these audio samples gets copied to kernel mode? Can someone explain me on this? Is it possible to capture the timestamps for the first and last audio samples that arrive at the driver level? Can I consider the .trigger(for playback & capture) callback in SNDRV_PCM_TRIGGER_START case is timestamp for the first audio sample? Similarly does .trigger callbacks SNDRV_PCM_TRIGGER_STOP gives the last audio sample timestamp? Thanks,

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How kernel derive irq number for particular irq line
by Abhinav Misra June 25, 2018

June 25, 2018

Hi Guys, I want to know how the irq number is derived in linux kernel. In kernel we are using below function for registering ISR. int *request_threaded_irq*(unsigned int irq, irq_handler_t handler, irq_handler_t thread_fn, unsigned long irqflags, const char *devname, void *dev_id) 1st arg is irq number. Now suppose for an i2c device, want to configure an interrupt then we can enable interrupt by configuring the particular register but from where we will get the irq number details. Do we as a programmer need to map it ? Please provide your views. BR,Abhinav

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tags
by Tobin C. Harding June 25, 2018

June 25, 2018

Hi, A question relating to 'Acked-by:' and tags in general please. Relates to Documentation/process/submitting-patches.rst (sections 12 through 14). For discussion, say a two patch series goes to version six and is then applied to some maintainers tree. On version three patch one of the series gets acked. On version four should patch one include the acked-by tag: - If patch one is unmodified? - If patch one is _trivially_ modified (update comment string etc)? Finally, if version 6 (the version that is _correct_) gets an acked-by on patch two does this final acked-by tag get included in the commit log? The only two ways I can see this happening both seem wrong, hence my question? - Developer submits another version with the tag. - Maintainer adds the tag when applying the series. If the tag does not make its way into the commit log this implies that the tag (and other tags?) are temporal and are mainly used by maintainers at the time of merging patches? Is this a fair comment? However, from the documentation the 'Cc' tag is meant to keep a record that a developer was included in the conversation and had opportunity to comment but did not i.e. this tag is _not_ temporal but is a permanent record. Thanks in advance, Tobin.

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How to debug video in the Linux Kernel?
by John Whitmore June 24, 2018

June 24, 2018

Hello all, I'm running OpenSUSE Tumbleweed so I'm just using their stock 4.16.12-1-default kernel at the moment. I'm not sure what has changed recently in their system but I'm having problems with video devices. This is a laptop with a single built in USB Camera, but for some reason two devices are created for that device: $ ls /dev/vid* /dev/video0 /dev/video1 I don't really use that camera but I then have a HDMI to USB capture device which I do use. When that's plugged in again I get two devices created, which I could live with, but the bigger problem is that the video being captured is not the full resolution of the camera connected. I'm displaying the camera's video with vlc and it's only displaying about 1/2 of the screen and totally distorted. The capture device is a MAGEWELL: [ 9033.836808] usb 2-4: new SuperSpeed USB device number 2 using xhci_hcd [ 9033.857976] usb 2-4: New USB device found, idVendor=2935, idProduct=0001 [ 9033.857983] usb 2-4: New USB device strings: Mfr=1, Product=2, SerialNumber=3 [ 9033.857988] usb 2-4: Product: XI100DUSB-HDMI [ 9033.857991] usb 2-4: Manufacturer: Magewell [ 9033.857995] usb 2-4: SerialNumber: A201161110153 [ 9033.859190] uvcvideo: Found UVC 1.00 device XI100DUSB-HDMI (2935:0001) [ 9033.860466] input: XI100DUSB-HDMI: XI100DUSB-HDMI as /devices/pci0000:00/0000:00:14.0/usb2/2-4/2-4:1.0/input/input26 [ 9033.862538] hid-generic 0003:2935:0001.0005: hiddev97,hidraw2: USB HID v1.01 Device [Magewell XI100DUSB-HDMI] on usb-0000:00:14.0-4/input4 [ 9034.432710] usbcore: registered new interface driver snd-usb-audio $ lsusb Bus 002 Device 002: ID 2935:0001 Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub Bus 001 Device 006: ID 0951:1643 Kingston Technology DataTraveler G3 Bus 001 Device 005: ID 046d:c52b Logitech, Inc. Unifying Receiver Bus 001 Device 002: ID 06cb:0078 Synaptics, Inc. Bus 001 Device 004: ID 8087:0aa7 Intel Corp. Bus 001 Device 003: ID 04f2:b5a7 Chicony Electronics Co., Ltd Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub *MOUSE* But now four video devices show up in /dev: $ ls /dev/vid* /dev/video0 /dev/video1 /dev/video2 /dev/video3 I've tried plugging both a digital camera into the HDMI capture device and the HDMI output of the laptop but in both cases I'm getting the same result a fraction of the screen and distorted. I've taken a screenshot and uploaded it so it might better describe what I'm seeing. So up above in this email I've added the text "*MOUSE*" my mouse if positioned on that word in the screen shot, but it doesn't come out in the screen capture as it didn't capture my mouse pointer. So in the screen capture you can see where my mouse is positioned over that text about half way down the screen of the laptop. If you then look at the VLC window which is displaying this captured video you can see the mouse pointer is right at the bottom of the captured video. https://pasteboard.co/HoMHNqa.png Maybe that problem is not in the kernel at all but vlc does display videos correctly. I've also been through all the vlc settings and can't find anything that makes a different. So given all that I'm wondering how I get to the problem with this? Searching for the words linux and video hasn't given me any insight as to how to locate the source of the problem. I'll revert to OpenSUSE Leap and see if I can't get back to having this working. Still I'd love to know how to resolve this issue, or at least shed some light on the source of the problem. John

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How to correctly load a driver without device tree?
by kipade June 21, 2018

June 21, 2018

Now, most of kernel device are initialized by its driver according by what described within device tree block. Here, the dtb was parsed and used during kernel booting. If so, I want to load a device driver after kernel booting using insmod, there would be no device tree block present, so, the device would not be configured correctly. so, how to make it usable? Regards, kipade.

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