July 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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kobj->state_initialized is never set to 0
by Helen Koike Aug. 10, 2018

Aug. 10, 2018

Hi, I am simulating hotplugging a platform device (to the media/platform/vimc driver), so I register it using platform_device_register, then I unregister it with platform_device_unregister, then I register it again, but the code doesn't allow me to register something that was registered before due to this line: https://github.com/torvalds/linux/blob/master/lib/kobject.c#L334 The variable kobj->state_initialized is set to 1 at https://github.com/torvalds/linux/blob/master/lib/kobject.c#L194 but it is never set to 0 again. Is this how it is supposed to work? Or kobj->state_initialized is set to 0 somewhere else I couldn't find? Thanks Helen

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Need Suggestions
by Athul Joy Aug. 2, 2018

Aug. 2, 2018

Dear friends, I am new to the Linux kernel development. Can anyone help me how to start my journey in order to build my own kernel?

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virtual address space allocation
by Babis Chalios Aug. 1, 2018

Aug. 1, 2018

Dear kernel hackers, I am working on the runtime system of a distributed memory programming language. For some reason we need to create a big hole on the address space of the application. We are trying to do so by using an mmap during the initialization of the runtime and then the runtime handles itself those addresses. This scenario works properly when the system allows memory overcommitment. More specifically, we seem to be fine if the /proc/sys/vm/overcommit_memory contains the values 0 or 1. However, we do have problems if memory overcommitment is disabled. So here goes the question: Is there any other mechanism to allow us to do what we want to? Things I 've thought so far: 1) To do my mmaps using PROT_NONE assuming that maybe those pages are not accounted for when calculating overcommitment. I did some tests and it seems that this assumption is wrong. 2) The possibility that there are addresses that are highly unlikely to be mapped in the address space of my application. If there is such an address range I could potentially relax the requirement that I should map all the address space at the beginning of the execution and instead try to mmap it progressively at runtime on a per-need basis. Any thoughts would be helpful. Cheers, Babis

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how to best ioremap() the ranges part of a "simple-bus" device?
by rpjday＠crashcourse.ca Aug. 1, 2018

Aug. 1, 2018

another (i suspect) fairly simple question, i've just never had the occasion to mess around in this part of the code. if i have a device tree source file containing the snippet: slave0: slave0-fubar@90000000 { compatible = "simple-bus"; ranges = <0x0 0x90000000 0x10000000>; #address-cells = <1>; #size-cells = <1>; }; slave1: slave1-fubar@a0000000 { compatible = "simple-bus"; ranges = <0x0 0xa0000000 0x10000000>; #address-cells = <1>; #size-cells = <1>; }; those two ranges actually represent physical addresses within an FPGA and, when certain events occur, i want some driver code to read/write some registers in slave0's address space, so obviously i'll need to access that device tree entry and effectively ioremap() slave0's physical address to a usable virtual address. is there a canonical way to do this? short of manually extracting the appropriate device tree node and reading that property and calling ioremap()? is there a wrapper for that sort of operation, which i imagine must be fairly common? oh, and a pointer to a good example in the current kernel source would, of course, be useful. rday

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what network driver routines are invoked via "ifup" and "ifdown"?
by rpjday＠crashcourse.ca July 31, 2018

July 31, 2018

first time poking around network drivers, and i'm wondering what platform driver routines are called when invoking ifup/ifdown from user space (if any). i'm *assuming* (possibly incorrectly) that the probe() and remove() routines are invoked only on loading and unloading the driver, not simple ifup and ifdown. guidance, anyone? rday

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OOM in secondary cgroup leading to networking loss
by Àbéjídé Àyodélé July 29, 2018

July 29, 2018

Hi friends, One one of our machines at work, we observed a sequence of events starting from an OOM in a secondary cgroup which ends up in the bond interface being down for a period of up to 12 seconds. Below is some piece of dmesg about when the bond interface went down: [Wed Jul 25 19:20:45 2018] Call Trace: [Wed Jul 25 19:20:45 2018] <IRQ> [Wed Jul 25 19:20:45 2018] ? dev_deactivate_queue.constprop.29+0x60/0x60 [Wed Jul 25 19:20:45 2018] call_timer_fn+0x30/0x120 [Wed Jul 25 19:20:45 2018] run_timer_softirq+0x3c8/0x420 [Wed Jul 25 19:20:45 2018] ? timerqueue_add+0x52/0x80 [Wed Jul 25 19:20:45 2018] ? enqueue_hrtimer+0x37/0x80 [Wed Jul 25 19:20:45 2018] ? recalibrate_cpu_khz+0x10/0x10 [Wed Jul 25 19:20:45 2018] __do_softirq+0xde/0x2b3 [Wed Jul 25 19:20:45 2018] irq_exit+0xae/0xb0 [Wed Jul 25 19:20:45 2018] smp_apic_timer_interrupt+0x70/0x120 [Wed Jul 25 19:20:45 2018] apic_timer_interrupt+0x7d/0x90 [Wed Jul 25 19:20:45 2018] </IRQ> [Wed Jul 25 19:20:45 2018] RIP: 0010:cpuidle_enter_state+0xa2/0x2e0 [Wed Jul 25 19:20:45 2018] RSP: 0018:ffffffff9c403eb0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff10 [Wed Jul 25 19:20:45 2018] RAX: ffff9075c0821a40 RBX: 0006cdb159b6000e RCX: 000000000000001f [Wed Jul 25 19:20:45 2018] RDX: 0006cdb159b6000e RSI: ffed6f2696159a35 RDI: 0000000000000000 [Wed Jul 25 19:20:45 2018] RBP: ffffd3edc100b900 R08: 0000000000000f48 R09: 0000000000000cfe [Wed Jul 25 19:20:45 2018] R10: ffffffff9c403e90 R11: 0000000000000f12 R12: 0000000000000003 [Wed Jul 25 19:20:45 2018] R13: ffffffff9c4b03d8 R14: 0000000000000000 R15: 0006cdb159783c8e [Wed Jul 25 19:20:45 2018] do_idle+0x181/0x1e0 [Wed Jul 25 19:20:45 2018] cpu_startup_entry+0x19/0x20 [Wed Jul 25 19:20:45 2018] start_kernel+0x400/0x408 [Wed Jul 25 19:20:45 2018] secondary_startup_64+0xa5/0xb0 [Wed Jul 25 19:20:45 2018] Code: 63 8e 60 04 00 00 eb 8f 4c 89 f7 c6 05 79 c7 b8 00 01 e8 00 7c fd ff 89 d9 48 89 c2 4c 89 f6 48 c7 c7 f0 38 28 9c e8 c7 a3 b6 ff <0f> 0b eb bd 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 57 41 56 [Wed Jul 25 19:20:45 2018] ---[ end trace 2ad2942fe3431402 ]--- [Wed Jul 25 19:20:45 2018] ixgbe 0000:19:00.1 eno2: initiating reset due to tx timeout [Wed Jul 25 19:20:45 2018] ixgbe 0000:19:00.1 eno2: Reset adapter [Wed Jul 25 19:20:48 2018] ixgbe 0000:19:00.0 eno1: initiating reset due to tx timeout [Wed Jul 25 19:20:53 2018] ixgbe 0000:19:00.0 eno1: initiating reset due to tx timeout We have observed a similar behavior on a 4.15.11 kernel we were running on a different machine, the current machine these logs are from runs a 4.14.52 kernel. A more detailed dmesg content can be found here: https://gist.github.com/bjhaid/49a1c58742ef2458984339503290ef9a I will appreciate any help in figuring out the cause and fix of this issue, or what the correct mailing list to post this to. Extra bit of information is the machines are Kubernetes nodes running docker. Thanks! Abejide Ayodele It always seems impossible until it's done. --Nelson Mandela

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Kernel API's for ADC
by chandrasekhar July 26, 2018

July 26, 2018

Hi, Are there any kernel API's for ADC. I am using NXP IMX6UL processor. I have to read ADC values in kernel space instead of sysfs/userspace. Thanks and Regards, Chandrasekhar

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Netpoll APIs
by jitendra kumar khasdev July 25, 2018

July 25, 2018

Hi All, Can netpoll apis send data over the internet. It worked for me in local network but when I try to send data over server which is in cloud not able to send it. Can anybody help me out ? --- Jitendra

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link_path_walk/dentry_path_raw TOCTTOU race question
by riya khanna July 25, 2018

July 25, 2018

Hi, I'm trying to understand what prevents TOCTTOU race conditions in dentry_path_raw and link_path_walk? What happens when somebody points a symlink path component from a dir that has the attacker is allowed to read to a dir that they are not allowed to read while link_path_walk() is doing its job? Thanks! -Riya

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