May 2020 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Hints for finding the hardware connected to staging drivers
by Sebastian Fricke May 18, 2020

May 18, 2020

Hi, I currently have a hard time to search for the real hardware behind some of the staging drivers. For example within the 'kpc2000' driver, only the Kconfig file gives a hint a to the manufacturer 'Daktronics'. But a google search for 'Daktronics kpc2000' or 'Daktronics kp2000' yields nothing. So, is there some kind of datasheet for those information? Or do I approach this problem incorrectly? Thank you in advance. Greetings Sebastian

1 0

Re: sound over USB
by Subhashini Rao Beerisetty May 14, 2020

May 14, 2020

On Wed, May 13, 2020 at 8:53 PM Sid Spry <sid(a)aeam.us> wrote: > > On Tue, May 12, 2020, at 11:43 AM, Subhashini Rao Beerisetty wrote> > > > > How do I use it for playing and recording an audio? > > > > Basically first I want to gain knowledge on set of test cases I can > > run on ALSA and then learn ALSA kernel modules stuff including > > snd_usb_audio mdule. > > > > So please guide me by providing related documentation/Steps. > > > > Hi, searching for an ALSA tutorial will get you far. However on a modern Linux distribution you will likely want to target pulseaudio. There are other libraries like RtAudio or PortAudio that may be easier to use and are cross platform. > > ALSA seems to give the most reliable results when enumerating audio devices. This can be done when pulseaudio is installed. The pulseaudio results are harder to interpret. > > In my experience, and not necessarily targeted at you, I have experienced massive difficulties getting RtAudio and PortAudio working in a reproducible way. ALSA is the most reliable but an unusual configuration, and pulseaudio is a hot complicated mess. > > > For what it's worth, the sound API on Linux is so pointlessly complex that I have, in the past, created a custom USB driver to avoid going through the sound API. It was easier to use libusb and get raw samples. Great. Does the custom USB driver is available in public repository?

1 0

sound over USB
by Subhashini Rao Beerisetty May 13, 2020

May 13, 2020

Hi all, In my Linux machine, I connected the plantronics usb headset with mic and I see(with the help of dmesg) that this device detected. [116676.507868] usb 2-2: new full-speed USB device number 5 using xhci_hcd [116676.923445] usb 2-2: New USB device found, idVendor=047f, idProduct=c012 [116676.927091] usb 2-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0 [116676.934252] usb 2-2: Product: Plantronics .Audio 628 USB [116676.941445] usb 2-2: Manufacturer: Plantronics [116676.945731] usb 2-2: ep 0x84 - rounding interval to 64 microframes, ep desc says 80 microframes [116677.078071] hidraw: raw HID events driver (C) Jiri Kosina [116677.159669] usbcore: registered new interface driver usbhid [116677.161686] usbhid: USB HID core driver [116677.175458] input: Plantronics Plantronics .Audio 628 USB as /devices/pci0000:00/0000:00:14.0/usb2/2-2/2-2:1.3/0003:047F:C012.0001/input/input4 [116677.234588] plantronics 0003:047F:C012.0001: input,hiddev0,hidraw0: USB HID v1.00 Device [Plantronics Plantronics .Audio 628 USB] on usb-0000:00:14.0-2/input3 [116677.281756] usbcore: registered new interface driver snd-usb-audio The following nodes are present in the /dev/snd $ ls -l /dev/snd/ total 0 drwxr-xr-x 2 root root 60 May 12 11:32 by-id drwxr-xr-x 2 root root 60 May 12 11:32 by-path crw-rw---- 1 root audio 116, 2 May 12 11:32 controlC1 crw-rw---- 1 root audio 116, 4 May 12 11:32 pcmC1D0c crw-rw---- 1 root audio 116, 3 May 12 11:32 pcmC1D0p crw-rw---- 1 root audio 116, 1 May 12 11:32 seq crw-rw---- 1 root audio 116, 33 May 12 11:32 timer What are all these devices present in /dev/snd How do I use it for playing and recording an audio? Basically first I want to gain knowledge on set of test cases I can run on ALSA and then learn ALSA kernel modules stuff including snd_usb_audio mdule. So please guide me by providing related documentation/Steps. Thanks,

3 2

First patch questions (target mailing list, target tree)
by Wojciech Kudla May 11, 2020

May 11, 2020

Hi, I'd like to send a patch to arch/x86/kernel/smp.c but I'm not sure about 2 details: 1) which branch of whose tree do I crate the patch against? According to MAINTAINERS: M: Thomas Gleixner <tglx(a)linutronix.de> M: Ingo Molnar <mingo(a)redhat.com> R: "H. Peter Anvin" <hpa(a)zytor.com> M: x86(a)kernel.org L: linux-kernel(a)vger.kernel.org T: git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/core Is this the right branch and the correct tree? 2) how do I access archives of x86@kernel.org? Thanks!

3 4

Why my patch in lore archive doe not have mbox?
by Lev R. Oshvang . May 8, 2020

May 8, 2020

Some time ago I posted patch to linux-integrity https://lore.kernel.org/linux-integrity/20200330122434.GB28214@kl/ 2 questions: 1. Linux-integrity maintainer, Mimi Zohar, rule this patch out. How can I arque with this ruling? 2. Why this patch does not have mbox.gz ? Thanks, Lev

2 1

queue_depth of the block device
by Oleksii Kurochko May 7, 2020

May 7, 2020

Hi all, I would like to understand how actually queue_depth parameter is set. I need this information to understand how can I affect on nr_request parameter from here https://elixir.bootlin.com/linux/latest/source/block/blk-mq-sched.c#L541. I have found that for my block device queue_depth is set equal to 1 so nr_request is equal to 2 but before the patch 32825c45("blk-mq-sched: fix performance regression of mq-deadline") was introduced it had been equal to 128 and because of nr_request is equal to 2 now it affects the performance of read/write operations. When I switched it back to 128 it starts to work as it was before. Currently, I am looking for a driver where is q->tag_set->queue_depth initialized. I found that for the block device is used sd driver using the next command: udevadm info -a /dev/sdb ... looking at parent device '/devices/pci0000:00/0000:00:14.0/usb3/3-3/3-3.1/3-3.1:1.0/host6/target6:0:0/6:0:0:0': KERNELS=="6:0:0:0" SUBSYSTEMS=="scsi" DRIVERS=="sd" .... So I decided to go sd_probe and try to understand how struct request_queue *q from blk_mq_init_sched() function is gotten and from sd_probe() function I can conclude that it is passed through ( https://elixir.bootlin.com/linux/latest/source/drivers/scsi/sd.c#L3388) device_add_disk() -> __device_add_disk() -> elevator_init_mq() -> blk_mq_init_mq() using gd variable. The queue for gd variable is set here https://elixir.bootlin.com/linux/latest/source/drivers/scsi/sd.c#L3360 so we can see that is actually taken value from a scsi_device structure. My question is how to find out a driver of a scsi_device? Am I correct that queue_depth should be set somewhere in the scsci_device? -- Best regards, Oleksii

1 0

Where is run_node defined in the sched_fair.c of Linux 2.6.33?
by Sreyan Chakravarty May 6, 2020

May 6, 2020

I am reading Robert Love's Book Linux Kernel Development( https://rads.stackoverflow.com/amzn/click/com/B003V4ATI0) It uses the 2.6.33 kernel for demonstration. I have been going through certain parts of the source and can't find out where is the initial definition of many things. A lot of things are just used, like "magic" without me finding the definition. One example: static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq) { struct rb_node *left = cfs_rq->rb_leftmost; if (!left) return NULL; return rb_entry(left, struct sched_entity, run_node); } static struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq) { struct rb_node *last = rb_last(&cfs_rq->tasks_timeline); if (!last) return NULL; return rb_entry(last, struct sched_entity, run_node); } This in kernel/sched_fair.c lines 384 and 394 in 2.6.33 kernel. Where is the run_node coming from ? I have grep ed( https://livegrep.com/search/linuxq=run_node&fold_case=auto&regex=false&cont… <https://livegrep.com/search/linux?q=run_node&fold_case=auto&regex=false&con…>) the entire source base over here, and I have not found any definition of run_node that would allow it to be used like this. There is a declaration( https://github.com/torvalds/linux/blob/219d54332a09e8d8741c1e1982f5eae56099…) in the sched_entity structure, but nothing outside of it that would allow it to be used like this. I cannot understand how things are organized, its really confusing. What is going on ? -- Regards, Sreyan Chakravarty

3 2

Why is there conflicting information out there for asmlinkage ?
by Sreyan Chakravarty May 6, 2020

May 6, 2020

I thought that all C programs normally use the stack for function calls. That's why in most languages if you are stuck in an infinite recursion you get a "Stack Overflow Error". If that is true, then what is so special about asmlinkage, it tells the program to look for variables in the stack rather than registers. The runtime does not look for values in the register in the first place. The asmlinkage tag is one other thing that we should observe about this > simple function. This is a #define for some gcc magic that tells the > compiler that the function should not expect to find any of its arguments > in registers (a common optimization), but only on the CPU's stack. What's even more strange is that when you learn that it is implemented using regparam in x86. https://qr.ae/pNy1wL The documentation for regparam is as follows: https://gcc.gnu.org/onlinedocs/gcc/x86-Function-Attributes.html#x86-Functio… > On x86-32 targets, the regparm attribute causes the compiler to pass > arguments number one to number if they are of integral type in registers > EAX, EDX, and ECX instead of on the stack. Functions that take a variable > number of arguments continue to be passed all of their arguments on the > stack. It says just the opposite. What is going on ? Which is correct the stack or the registers ? Why is there conflicting info out there ? -- Regards, Sreyan Chakravarty

3 2

Location of files for a new driver
by Jacko Dirks May 5, 2020

May 5, 2020

Hello, I am starting to work on a new driver. I think the actual driver (c file) needs to be placed in drivers/staging/subdir (am I correct?). But I also need to edit existing dts and dtsi files and I also need to introduce a new overlay. Where do I place those changes and new files? Thanks in advance, Jacko Dirks

2 3

the same name of external kernel module as one of source file
by Tomek The Messenger May 5, 2020

May 5, 2020

Hi If I have something like this in makefile: obj-m := reset-core.o reset-core-y := reset-core-main.o reset-core-utils.o then module is built OK. If I have something like that: obj-m := reset-core.o reset-core-y := reset-core.o reset-core-utils.o then it is wrongly built. So I will replace all source file characters '-' to '_' and I will have: obj-m := reset-core.o reset-core-y := reset_core.o reset_core_utils.o and everything will be OK, but it is a bit frustrating that code rules me instead of me rules code. Maybe there is another solution?

2 1