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searching for a missing driver
by Hugo Lefeuvre May 24, 2018

May 24, 2018

Hi, I've been reading documentation about linux drivers development for quite a while now, but never did anything really useful of it. Lack of time, but most importantly lack of projects to apply this knowledge. Now I've got some spare time ahead of me, and it seems to be the right moment to start a kernel driver project. ... but I don't know exactly what kind of device driver I want to write, and what kind of device I want to work on. I think I could have fun working on usb drivers, expecially after reading this blog post[0], but I don't know if it's the best for a first driver project. Is there a place where I can find a list of devices missing kernel drivers ? Can you recommend me a type of device I should opt for, given that this is going to be my first driver project ? A specific device ? Having to reverse engineer stuff isn't much of a problem for me, as long as it doesn't get too far into the "black magic" land. ;) Also, if you have any kind of advices for people starting their first driver project, I'd be glad to hear them. Thanks ! Cheers, Hugo [0] http://matthias.vallentin.net/blog/2007/04/writing-a-linux-kernel-driver-fo… -- Hugo Lefeuvre (hle) | www.owl.eu.com 4096/ 9C4F C8BF A4B0 8FC5 48EB 56B8 1962 765B B9A8 BACA

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Please add new user to Wiki editors list
by Alexey Brodkin May 23, 2018

May 23, 2018

Hello, As one of sub-maintainers of Linux port for ARC architecture I'd like to be able to add information about ARC-related changes in Linux kernel changelogs (https://kernelnewbies.org/LinuxVersions) Could you please add my username AlexeyBrodkin to the EditorsGroup? -Alexey P.S. If of any interest (sorta to confirm I'm not a bot these are my contributions in the kernel development so far: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/?qt=…)

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sound: ALSA PCM Timestamps
by Muni Sekhar May 23, 2018

May 23, 2018

[ Please keep me in CC as I'm not subscribed to the list] Hi All, There are several time stamping functions in ALSA: snd_pcm_status_get_trigger_tstamp snd_pcm_status_get_trigger_htstamp snd_pcm_status_get_tstamp snd_pcm_status_get_htstamp snd_pcm_status_get_audio_htstamp snd_pcm_status_get_driver_htstamp I would like to understand what points in time the resulting functions represent and what is the corresponding kernel mode callback for those API’s. I'd be really grateful if someone took the time to help me clearing my doubt. -- Thanks, Sekhar

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Fwd: New to the Kernel Newbie
by Janakiramireddy Tamma May 22, 2018

May 22, 2018

Hello, I am completely new to the kernel newbie, can some one help me where can I get started. Thanks Janaki Rami Reddy

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Re: Delivery Status Notification (Failure)
by Pintu Kumar May 21, 2018

May 21, 2018

On Fri, May 11, 2018 at 6:34 PM, Lucas Stach <l.stach(a)pengutronix.de> wrote: > Am Freitag, den 11.05.2018, 13:39 +0100 schrieb Russell King - ARM Linux: >> On Fri, May 11, 2018 at 05:07:37PM +0530, Pintu Kumar wrote: >> > Hi, >> > >> > I need one help. >> > I am using i.MX7 Sabre board with kernel version 4.1.15 >> > >> > Let's say I am interested in GPIO number: 21 >> > I wanted to set CPU affinity for particular GPIO->IRQ number, so I >> > tried the below steps: >> > root@10:~# echo 21 > /sys/class/gpio/export >> > root@10:~# echo "rising" > /sys/class/gpio/gpio21/edge >> > root@10:~# cat /proc/interrupts | grep 21 >> > 47: 0 0 gpio-mxc 21 Edge gpiolib >> > root@10:~# cat /sys/class/gpio/gpio21/direction >> > in >> > root@10:~# cat /proc/irq/47/smp_affinity >> > 3 >> > root@10:~# echo 2 > /proc/irq/47/smp_affinity >> > -bash: echo: write error: Input/output error >> > >> > But I get input/output error. >> > When I debug further, found that irq_can_set_affinity is returning 0: >> > [ 0.000000] genirq: irq_can_set_affinity (0): balance: 1, >> > irq_data.chip: a81b7e48, irq_set_affinity: (null) >> > [ 0.000000] write_irq_affinity: FAIL >> > >> > I also tried first setting /proc/irq/default_smp_affinity to 2 (from 3). >> > This change is working, but the smp_affinity setting for the new IRQ >> > is not working. >> > >> > When I try to set smp_affinity for mmc0, then it works. >> > # cat /proc/interrupts | grep mmc >> > 295: 55 0 GPCV2 22 Edge mmc0 >> > 296: 0 0 GPCV2 23 Edge mmc1 >> > 297: 52 0 GPCV2 24 Edge mmc2 >> > >> > root@10:~# echo 2 > /proc/irq/295/smp_affinity >> > root@10:~# >> > >> > >> > So, I wanted to know what are the conditions for which setting >> > smp_affinity for an IRQ will work ? >> > >> > Is there any way by which I can set CPU affinity to a GPIO -> IRQ ? >> > Whether, irq_set_affinity_hint() will work in this case ? >> >> IRQ affinity is only supported where interrupts are _directly_ wired to >> the GIC. It's the GIC which does the interrupt steering to the CPU >> cores. >> >> Interrupts on downstream interrupt controllers (such as GPCV2) have no >> ability to be directed independently to other CPUs - the only possible >> way to change the mapping is to move _all_ interrupts on that controller, >> and any downstream chained interrupts at GIC level. >> >> Hence why Interrupt 295 has no irq_set_affinity function: there is no way >> for the interrupt controller itself to change the affinity of the input >> interrupt. > > The GPCv2 though is a secondary IRQ controller which has a 1:1 mapping > of its input IRQs to the upstream GIC IRQ lines. Affinity can thus be > handled by forwarding the request to the GIC by > irq_chip_set_affinity_parent(). > > As this is handled correctly in the upstream kernel since the first > commit introducing support for the GPCv2, it seems the issue is only > present in some downstream kernel. > OK. Thanks so much for your reply. I saw some of the drivers using irq_set_affinity_hint() to force the IRQ affinity to a particular CPU. This is the sample: { cpumask_clear(mask); cpumask_set_cpu(cpu, mask); irq_set_affinity_hint(irq, mask); } Whether this logic will work for a particular GPIO pin ? > Regards, > Lucas

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sound: latency and synchronization measurements
by Muni Sekhar May 18, 2018

May 18, 2018

[ Please keep me in CC as I'm not subscribed to the list] Hi All, I am trying to characterize the audio synchronization between two systems. There is a mechanism to route audio between two systems, we run ‘aplay’ at one system and ‘arecord’ in other system. We need to measure the time difference when audio sample is out at one port and arriving at another port in different system. I plan to add printk’s in “struct snd_pcm_ops” call backs, but does these call backs tells when it received first and last audio frames\samples? Or else please suggest any other best method. -- Thanks, Sekhar

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How to include two bootup logos in the kernel and choose which one to load via kernel bootup arguments
by Davis Roman May 15, 2018

May 15, 2018

Hello, I have two identical embedded devices where the only difference is one has a 5" screen and the other has a 7" screen. Currently I created a custom boot up screen for our 7" version and stored it in drivers/video/logo/logo_custom_clut224.ppm. On bootup, it shows up fine. Now I would like to figure out how to create another bootup screen for the 5" version and store it in the kernel as well ( perhaps drivers/video/logo/logo_custom_clut224-5in.ppm ) In u-boot, I can detect which version I have by poking our devicetree blob however I'm not sure how I would dynamically tell the kernel which image to use. Any ideas regarding how to do this would be greatly appreciated. Thank you, Davis

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Re: Eudyptula (Was: Kernelnewbies Digest, Vol 89, Issue 14)
by Aleix Roca Nonell May 14, 2018

May 14, 2018

On Wed, May 02, 2018 at 04:55:09PM +0200, Aleix Roca Nonell wrote: > On Thu, Apr 26, 2018 at 10:01:18PM +0100, justin.skists(a)juzza.co.uk wrote: > > > > > On 20 April 2018 at 07:28 Aleix Roca Nonell <kernelrocks(a)gmail.com> wrote: > > > > > > I just wanted to ask the same question. I'm still doing the challenge > > > but it has been amost two months since I sent my last solution and > > > there has not been any answer yet (except the usual auto-response of > > > task received). Does somebody knows if it is still alive even for old > > > challengers? > > > > I usually get a response when I'm about to go on holiday or AFK for a > > few days or so! :) > > > > You need to remember that the maintainers who run the challenge are > > very busy people. The merge window for 4.17 was recently closed (and > > before that was the Spectre/Meltdown mess) so the maintainers are > > probably catching up on patches in their inbox. > > > > Justin. > > Oh! I understand. Thank you very much! :) In fact, I received a response > just a few days ago, so the challenge continues! > > Thank you Justin! :) Sorry I messed it up with mutt and sent the last reply only to Justin -_-'

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Ioctl TCSBRK in a ldisc driver
by Oliver Graute May 14, 2018

May 14, 2018

Hello list, I try to handle some ioctl by my ldisc driver. Especially ioctl TCSBRK. After wondering why I didn't receive TCSBRK ioctl I stumbled accros this comments: include/linux/tty_ldisc.h * int (*ioctl)(struct tty_struct * tty, struct file * file, * unsigned int cmd, unsigned long arg); * * This function is called when the user requests an ioctl which * is not handled by the tty layer or the low-level tty driver. * It is intended for ioctls which affect line discpline * operation. Note that the search order for ioctls is (1) tty * layer, (2) tty low-level driver, (3) line discpline. So a * low-level driver can "grab" an ioctl request before the line * discpline has a chance to see it. and the corresponding tty_ioctl() implementation in tty_io.c. Am I correct that the TCSBRK is grabbed here before receiving it in any ldisc driver code? Is there a way to change the order without major changes in the tty_io.c code? I want to intercept the TCSBRK because my hardware needs some handling here and for userspace applications it should be transparent. Best regards, Oliver

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Regarding Audio Drivers
by Divanshu Singh May 12, 2018

May 12, 2018

Respected Reader I am a long time Linux user. I am a full-time web developer but I have some knowledge of C, C++ and bit of x86 assembly. I have 4 Linux system at my home - a MacBook Air, 2 HP and 1 Dell and recently I found that none of them is able to detect or work with an external microphone. I have tried every possible configuration in ALSA that made sense but nothing worked. I also tried re-installing drivers for my sound cards. Searching the Internet, I realized that I am not alone there are thousands of Linux users who face the same problem. I found this long answer explaining why this problem exists with Linux system. https://unix.stackexchange.com/questions/381071/headphones-with-combo-jack-… Many Linux users switch to windows just because of a microphone issue. I am frustrated and want to end this for once and all. I have never written a driver but I am a quick learner and have lots of patience. Please guide me with following: - Getting started with drivers - Learn about ALSA enough to make contributions to it With regards Divanshu

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