May 2016 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

make oldconfig forces HWMON to be inbuilt
by Ani Sinha May 25, 2016

May 25, 2016

Hi guys : I am seeing this weird issue where even though my original kernel configuration tries to build HWMON as a module, when I do 'make oldconfig', it forces HWMON to be built into the kernel. Is there anyway I can find what configuration is forcing this change? CONFIG_HWMEM is a tristate symbol. thanks ani

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Request for guidance
by Abhishek May 24, 2016

May 24, 2016

Hi All, I am an Embedded Software Engineer with 3+ years of experience. I am fascinated by kernel development and want to be a device driver developer. I have done following so far. #Studied LDD3. #Subscribed to eudyptula challenge and submitted solution for 4th task(waiting for next task). #Have compiled and installed kernel successfully on multiple boards. I want to start contributing to kernel so I looked into staging and found that I can not work on TODO unless I have required hardware to test patch (which unfortunately I don't have). Requesting you to guide me about how to start working on kernel/device drivers development. Thanks, Abhishek

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Changing the default scheduler
by Renato Utsch May 24, 2016

May 24, 2016

Hello, I am a new developer trying to learn how to tinker with the kernel. I searched on the internet but couldn't find much info about this (and couldn't find any info up to date). My question is, how does the kernel decide which is the default scheduler that all processes start with? I can change the scheduler of a process by sched_setscheduler(), but how do I change *all* processes from using the CFS scheduler to, for example, the RR scheduler? Sorry if this is too basic, but I don't know where to search for this. If you guys could point me places where I can learn more about this, I would be grateful.

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is there any actual usage of the device tree node "/chosen@0"?
by Robert P. J. Day May 23, 2016

May 23, 2016

currently perusing the kernel code for device tree processing and stumbled across this in drivers/of/base.c: void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) { struct property *pp; of_aliases = of_find_node_by_path("/aliases"); of_chosen = of_find_node_by_path("/chosen"); if (of_chosen == NULL) of_chosen = of_find_node_by_path("/chosen@0"); ????? if (of_chosen) { ... snip ... that pretty clearly says that "/chosen@0" is an equivalent node name for "/chosen", correct? but why was that equivalence first defined? if i scan the entire kernel source tree, this is all i get: $ grep -r "/chosen@0" * arch/powerpc/boot/oflib.c: chosen = of_finddevice("/chosen@0"); drivers/of/base.c: of_chosen = of_find_node_by_path("/chosen@0"); drivers/of/fdt.c: offset = fdt_path_offset(fdt, "/chosen@0"); $ so there are apparently three files that *check* for that alternate name, but not a single .dts or .dtsi that actually uses it. is there any value to that alternate name? 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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Finding GPIO names under Linux
by Johannes Thoma May 23, 2016

May 23, 2016

Dear list, I am writing a driver which uses the "new" descriptor interface of the GPIO library. As far as I have understood it, gpiod_get(8) is the way to allocate (and also lock?) GPIOs pins for use. My question is how do I find what to pass as the con_id parameter (this should identify the pin but please correct me if I am wrong, in that case how to I tell gpiod_get which pin I want?). Is there a file somewhere where I can find the pin names of my hardware (which is a raspberry 1 for now), something like /sys/class/gpio/xxx/gpio_pin_names or so, or do I have to look them up in the device tree or somewhere else? Or do I have to configure the pin somewhere in the device tree? What I would like to do is offer an interface (via configfs) where the pins the sensor is attached can be configured dynamically at run-time. The driver itself is OpenSource (GPL) and can be obtained at http://github.com/johannesthoma/linux-hc-sro4 (iio branch is currently the dev branch where this problem occurs). Thanks a lot, - Johannes

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git send-email
by Tobin Harding May 22, 2016

May 22, 2016

Workflow - $ git format-patch -s -1 add patch comment then $ git send-email Question please - Who should the email be sent to without having a 'To' address repeated in the CC field generated by `git send-email`. To rephrase the question: git send-email CC's everyone who may be interested according to get_maintainers.pl. Will I annoy people if I address them in the To field as well as the CC field. Thank you in advance for your time, Tobin Harding.

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what is the point of "dt-bindings" symlinks under some arches?
by Robert P. J. Day May 22, 2016

May 22, 2016

i'm curious about the value of the small number of "dt-bindings" symlinks under some architectures that all simply link to the top-level include/dt-bindings/ directory: $ find . -name dt-bindings -exec ls -ld {} \; lrwxrwxrwx. 1 rpjday rpjday 34 Apr 26 13:07 ./arch/cris/boot/dts/include/dt-bindings -> ../../../../../include/dt-bindings lrwxrwxrwx. 1 rpjday rpjday 34 Apr 25 10:58 ./arch/powerpc/boot/dts/include/dt-bindings -> ../../../../../include/dt-bindings lrwxrwxrwx. 1 rpjday rpjday 34 Apr 25 10:57 ./arch/metag/boot/dts/include/dt-bindings -> ../../../../../include/dt-bindings lrwxrwxrwx. 1 rpjday rpjday 34 Apr 25 10:57 ./arch/arm64/boot/dts/include/dt-bindings -> ../../../../../include/dt-bindings lrwxrwxrwx. 1 rpjday rpjday 34 Apr 25 10:57 ./arch/arm/boot/dts/include/dt-bindings -> ../../../../../include/dt-bindings lrwxrwxrwx. 1 rpjday rpjday 34 Apr 25 10:57 ./arch/mips/boot/dts/include/dt-bindings -> ../../../../../include/dt-bindings drwxrwxr-x. 26 rpjday rpjday 4096 Apr 26 13:07 ./include/dt-bindings $ normally, i expect to see setups like that in cases where, historically, an architecture kept track of its own content and, at some point, it was centralized, so the previous directory (whatever it contained) was simply replaced by a symlink. but even without that arch-specific symlink, wouldn't the top-level include/dt-bindings/ directory be searched, anyway? or maybe not, i guess i'll check the Makefile to see if it would be. thoughts? given that all those symlinks are absolutely identical, couldn't they all just be removed? 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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Management of duplicate commits in public repository
by William Breathitt Gray May 21, 2016

May 21, 2016

I'm curious how subsystem maintainers typically handle duplicate commits in their public subsystem repositories. I'm referring to commits which appear originally in their branch, but are cherry-pick'd to another subsystem maintainer's repository, and then later merged back in; this leads to the same textual changes appearing as two distinct commits after the merge. In my workflow, I typically rebase against the public repository before I submit my patches to the subsystem maintainer. In this scenario, the rebase drops commits which do not produce textual changes in my tree. Thus, I never have duplicate commit messages in my private repository. However, a subsystem repository is public, so subsystem maintainers typically merge new releases of the Linux kernel, rather than rebase, since history should not be written. If merges are continually performed, will the subsystem repository not gradually accumulate duplicate commits over time? Are the duplicate commits simply accepted as the cost of operating a public repository, or do the subsystem maintainers make an effort to remove them before the merge? William Breathitt Gray

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if block style when condition spams to multiple lines.
by Daniel. May 20, 2016

May 20, 2016

What is the preferred way to ident if statement when the condition spams to multiple lines, ex: if (cond1 && cond2 && cond3) { ... ... } or if (cond1 && cond2 && cond3) { ... ... } or if only one statement inside body if (cond1 && cond2 && cond3 ... Also, usualy, I align the remaining lines from codition to one column after the parenthesis that starts the condition and usually I need spaces to do that. Is that okay? With no spaces would be: if (cond1 && cond2) { ... Regards, -- *"Do or do not. There is no try"* *Yoda Master*

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TEA5767 FM driver issue
by Aric May 18, 2016

May 18, 2016

hi, I'm working on using fm tea5767 module. But, I found it already have driver, in drivers/media/common/tuners/tea5767.c . I resiger a i2c board info in arch/arm/mach-xxxx, but only found a i2c device in /sys/bus/i2c/devices/0-0060. The driver and device not going to match !! Anyonre can help ? Seems the driver was not called, how to trigger the driver match procedure ? Thx!! /BRs

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