- kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Inquiry Regarding Handling of Kernel Crashes
by Muni Sekhar May 12, 2024

May 12, 2024

Dear Linux Kernel Community, I hope this email finds you well. I am currently engaged in testing device drivers in Linux kernel mode, and I have encountered various types of kernel crashes during my testing process. Among these, some examples of kernel crashes include OOPS, lockups and others. I have a few questions regarding the handling of kernel crashes during testing: When encountering a kernel crash during testing, is it advisable to continue testing without rebooting the system? Or is it preferable to reboot the system after each kernel crash and then resume testing? Can the first kernel crash, whether it is an OOPS, or any other type crash, potentially lead to subsequent crashes of the same or different types? If so, should debugging efforts focus only on the first kernel crash, or should all subsequent crashes also be considered and addressed? In the event that the system needs to be rebooted after a kernel crash, how can user space test utilities be informed that a kernel crash has occurred? Additionally, how can the system be configured to automatically reboot in the event of a kernel crash? I would greatly appreciate any insights or best practices you can share regarding the handling of kernel crashes during testing. Your expertise and guidance on this matter would be invaluable to my testing efforts. Thank you very much for your time and assistance. I look forward to your response. -- Thanks, Sekhar

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Regarding Linux Kernel Mentorship
by Manav May 12, 2024

May 12, 2024

Hi! I'm Manav Chauhan, a 3rd year Computer Science and Engineering student from India and I have an aim of working at CERN Labs one day where I can contribute to a place that drives scientific innovation where my interest lies in the domain of system/low-level as I have always been fascinated by the core or the internals of Computer Science. To achieve such an ambitious goal, I need some credibility and more experience in the field of low-level and operating systems. My research led me to the Linux Kernel Mentorship program where I read blogs and experiences of other such passionate individuals who contributed to such a core technology that is the linux kernel. I have been using Debian Testing for a year and am curious about how all of it works under the hood. Diving deep into this field may be daunting so I wanted some guidance regarding participation in this mentorship for the Fall program. I am already midway through the 'A Beginner's Guide to Linux Kernel Development (LFD103)' course and was looking forward to some guidance regarding other steps I should take to strengthen my application..

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spi: Inquiry Regarding Linux Kernel SPI Subsystem device drivers
by Subhashini Rao Beerisetty May 10, 2024

May 10, 2024

Hi all, I hope this email finds you well. I am new to the Linux kernel SPI subsystem, I am currently in the process of learning about its functionalities and intricacies. I have a few doubts and questions that I would like to clarify, and I am hoping you could provide some assistance. As I understand it, the Linux kernel SPI subsystem supports two main types of SPI drivers: SPI controller drivers and SPI protocol drivers. Much like the USB Skeleton driver (drivers/usb/usb-skeleton.c) serves as an excellent reference example for new engineers developing USB device drivers, I am wondering if there exists a similar skeleton driver for both SPI controller and SPI protocol drivers within the Linux kernel tree. Would it be possible for you to share any reference code or examples for these drivers? Additionally, I am curious about the interaction between user space applications and SPI hardware devices on the target side through the SPI protocol driver. Could you please clarify if user space applications communicate with the hardware device on the target side via the SPI protocol driver running on the host side? Furthermore, I would like to inquire about the availability of an SPI library for user space applications, similar to libusb for USB communication. Does the SPI subsystem provide any such library, or do user space applications communicate directly with the SPI protocol or controller driver through system call? Your insights into these matters would be immensely helpful for my understanding of the Linux kernel SPI subsystem. Thank you very much for your time and consideration. Thank You!

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Re: Seeking Assistance with Spin Lock Usage and Resolving Hard LOCKUP Error
by Billie Alsup (balsup) May 10, 2024

May 10, 2024

>From: Muni Sekhar <munisekharrms(a)gmail.com> >Here is a brief overview of how I have implemented spin locks in my module: > >spinlock_t my_spinlock; // Declare a spin lock > >// In ISR context (interrupt handler): >spin_lock_irqsave(&my_spinlock, flags); >// ... Critical section ... >spin_unlock_irqrestore(&my_spinlock, flags); > > >// In process context: (struct file_operations.read) >spin_lock(&my_spinlock); >// ... Critical section ... >spin_unlock(&my_spinlock); from my understanding, you have the usage backwards. It is the irqsave/irqrestore versions that should be used within process context to prevent the interrupt from being handled on the same cpu while executing in your critical section. The use of irqsave/irqrestore within the isr itself is ok, although perhaps unnecessary. It depends on whether the interrupt can occur again while you are servicing the interrupt (whether on this cpu or another). Usually (?) the same interrupt does not nest, unless you have explicitly coded to allow it (for example, by acknowledging and re-enabling the interrupt early in your ISR). Certainly the spinlock is necessary to protect the critical section from running in an isr on one cpu and process space on another cpu. >From a lockup perspective, not doing the irqsave/irqrestore from process context could explain your problem. Also look for code (anywhere!) that blindly enables interrupts, rather than doing irqrestore from a prior irqsave.

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Submitting a selftest patch
by Camila Alvarez May 8, 2024

May 8, 2024

I’ve been discussing a bug with one of the maintainers of a subsystem. At one point I was asked to craft a selftest for the issue. My question is: how do I send the patch with the selftest? Do I need to reference the email where the selftest request was made? Or should I just send it as an independent patch? Thanks in advance

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Re: ALSA: usb-audio: Adding mixer controls to Mbox3
by Takashi Iwai May 6, 2024

May 6, 2024

On Wed, 01 May 2024 16:31:35 +0200, Manu wrote: > > Thank you for all your help, Takashi! > > I would like to add the hardware mixer controls for Mbox3. > I have already identified every control in the function "mbox3_setup_defaults" > of "quirks.c", but I am unsure about the structure needed to make the controls > appear in alsamixer (further investigation is required). I would appreciate any > help you or anyone else can provide. I believe it'd be helpful if you can show some mock up or any examples you wanted to try (or had in your head). If the question was about the complexity or too many code to add there, you can split to another file, too. thanks, Takashi > > Manuel Barrio Linares > > > On Wed, May 1, 2024 at 4:55 AM Takashi Iwai <tiwai(a)suse.de> wrote: > > > > On Tue, 30 Apr 2024 19:10:18 +0200, > > Manuel Barrio Linares wrote: > > > > > > This adds support for all sample rates supported by the > > > hardware,Digidesign Mbox 3 supports: {44100, 48000, 88200, 96000} > > > > > > Fixes syncing clock issues that presented as pops. To test this, without > > > this patch playing 440hz tone produces pops. > > > > > > Clock is now synced between playback and capture interfaces so no more > > > latency drift issue when using pipewire pro-profile. > > > (https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/3900) > > > > > > Signed-off-by: Manuel Barrio Linares <mbarriolinares(a)gmail.com> > > > > Applied to for-next branch now. Thanks! > > > > > > Takashi

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Adding a device support
by Rémi ESSAISSI May 3, 2024

May 3, 2024

Hello I bought without checking its support a USB->VGA/HDMI adapter. the Fresco Logic FL2000 . Some code is at https://github.com/FrescoLogic/FL2000 . But unfortunately unusable as is. I would like to know if there is anything I can do to help getting it fully supported . Or if there is another platform/ML I can or should contact . Regards

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serial debug: permission denied
by carrollbryanm＠gmail.com April 27, 2024

April 27, 2024

Hi all, I'm attempting to use gdb to debug over a serial connection using two VM's. I'm getting a "Permission denied" when I try to connect over the serial com port. Gdb has the following output when I try to connect: Reading symbols from vmlinux... +target remote /dev/ttyS1 Remote debugging using /dev/ttyS1 [remote] start_remote_1: enter [remote] Sending packet: $qSupported:multiprocess+;swbreak+;hwbreak+;qRelocInsn+;fork-events+;vfork-e vents+;exec-events+;vContSupported+;QThreadEvents+;no-resumed+;memory-taggin g+#ec [remote] Junk: d [remote] Junk: i [remote] Junk: a [remote] Junk: g [remote] Junk: : [remote] Junk: [remote] Received Nak [remote] Sending packet: $qSupported:multiprocess+;swbreak+;hwbreak+;qRelocInsn+;fork-events+;vfork-e vents+;exec-events+;vContSupported+;QThreadEvents+;no-resumed+;memory-taggin g+#ec [remote] Junk: 2 [remote] Junk: 2 [remote] Junk: : [remote] Junk: [remote] Junk: P [remote] Junk: e [remote] Junk: r [remote] Junk: m [remote] Junk: i [remote] Junk: s [remote] Junk: s [remote] Junk: i [remote] Junk: o [remote] Junk: n [remote] Junk: [remote] Junk: d [remote] Junk: e [remote] Junk: n [remote] Junk: i [remote] Junk: e [remote] Junk: d [remote] Junk: ^M [remote] Junk: [remote] Junk: [ [remote] Junk: 2 [remote] Junk: ] [remote] Junk: k [remote] Junk: d [remote] Junk: b [remote] Junk: > [remote] Junk: [remote] Junk: : [remote] Junk: m [remote] Junk: u [remote] Junk: l [remote] Junk: t [remote] Junk: i [remote] Junk: p [remote] Junk: r [remote] Junk: o [remote] Junk: c [remote] Junk: e [remote] Junk: s [remote] Junk: s [remote] Received Ack [remote] read_frame: Bad checksum, sentsum=0xec, csum=0x8, buf=qSupporteddiag: -22: Permission denied\r\n[2]kdb> :multiprocess+;swbreak+;hwbreak+;qRelocInsn+;fork-events+;vfork-events+;exec -events+;vContSupported+;QThreadEvents+;no-resumed+;memory-tagging+ [remote] getpkt: Timed out. [remote] getpkt: Timed out. Ignoring packet error, continuing... [remote] packet_ok: Packet qSupported (supported-packets) is supported [remote] Sending packet: $vCont?#49 [remote] Received Nak [remote] Sending packet: $vCont?#49 [remote] Received Ack [remote] Packet received: vCont? [remote] packet_ok: Packet vCont (verbose-resume) is NOT supported [remote] packet_ok: Packet vCont (verbose-resume) is NOT supported [remote] Sending packet: $vMustReplyEmpty#3a [remote] putpkt_binary: Packet instead of Ack, ignoring it [remote] Received Ack [remote] Packet received: vMustReplyEmpty [remote] start_remote_1: exit Remote replied unexpectedly to 'vMustReplyEmpty': vMustReplyEmpty +quit It seems the target is denying permission. I've been searching around but have not found anything similar. I tried opening the permissions on the /dev/ttyS1 on both VM's to rwxrwxrwx and that doesn't help. There are no SELinux warnings on the debugger VM. I don't know if SELinux is causing a problem on the target VM. More details about the configuration: I'm running two Rocky 9.3 VM's on Windows Hyper-V that I have connected over a named pipe using the Powershell Set-VMComport commands: Set-VMComport -VMName "Rocky-Debugger" -Number 2 -Path \\.\pipe\rocky-pipe-2 <file://./pipe/rocky-pipe-2> Set-VMComport -VMName "Rocky " -Number 2 -Path \\.\pipe\rocky-pipe-2 <file://./pipe/rocky-pipe-2> I downloaded the 6.8.5 kernel from the kernel.org website and compiled it on the "Rocky" vm using the following configuration: # # Generic Kernel Debugging Instruments # CONFIG_MAGIC_SYSRQ=y CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x1 CONFIG_MAGIC_SYSRQ_SERIAL=y CONFIG_MAGIC_SYSRQ_SERIAL_SEQUENCE="" CONFIG_DEBUG_FS=y CONFIG_DEBUG_FS_ALLOW_ALL=y # CONFIG_DEBUG_FS_DISALLOW_MOUNT is not set # CONFIG_DEBUG_FS_ALLOW_NONE is not set CONFIG_HAVE_ARCH_KGDB=y CONFIG_KGDB=y CONFIG_KGDB_HONOUR_BLOCKLIST=y CONFIG_KGDB_SERIAL_CONSOLE=y CONFIG_KGDB_TESTS=y # CONFIG_KGDB_TESTS_ON_BOOT is not set CONFIG_KGDB_LOW_LEVEL_TRAP=y CONFIG_KGDB_KDB=y CONFIG_KDB_DEFAULT_ENABLE=0x0 CONFIG_KDB_KEYBOARD=y CONFIG_KDB_CONTINUE_CATASTROPHIC=0 CONFIG_ARCH_HAS_EARLY_DEBUG=y CONFIG_ARCH_HAS_UBSAN_SANITIZE_ALL=y # CONFIG_UBSAN is not set CONFIG_HAVE_ARCH_KCSAN=y CONFIG_HAVE_KCSAN_COMPILER=y # CONFIG_KCSAN is not set # end of Generic Kernel Debugging Instruments I added the kernel args "console=tty0 console=ttyS0,115200 kgdboc=ttyS1,115200". I start the VM with the new kernel and run the command "echo g > /proc/sysrq-trigger". On the "Rocky-debugger" vm, I added my user to "dialout". The permissions on /dev/ttyS1 is rw for the group. I set the following in .gdbinit, "set serial baud 115200". Run "gdb vmlinux", then "target remote /dev/ttyS1". That's when I get the "Permission denied". I can connect to the console over serial using "sudo screen ttyS0" and that works just fine. So I don't believe it's a Windows Hyper-V permissions issue. I'm out of ideas. Any help is appreciated! Thanks, Bryan Carroll

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Userspace or kernelspace driver once again
by Patryk April 27, 2024

April 27, 2024

Suppose that you want to use a driver that controls fans ,let's say max31785. You have two options to chose: - kernel space driver that is already available in mainline linux - userspace driver that comes from Hardware Abstraction Layer library that also has an implementation, the library is a primary hardware access library used by all our projects What would you choose? And why? And if "it depends..." then depends on what actually? Best regards Patryk

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Source code organization
by Billie Alsup (balsup) April 23, 2024

April 23, 2024

I have a set of drivers that I would like to upstream. These are primarily MFD style drivers supporting Cisco-8000 FPGAs. The devices can be instantiated through multiple top level drivers, which provide the access mechanism for the MFD driver. For example, an FPGA can be accessed via PCI, or via i2c, or via SLPC, or via P2PM (a point-to-point interface). We currently build these drivers out of tree, under a single directory drivers/cisco. I note that existing drivers are spread out across the kernel tree, sometimes by bus (pci, i2c), sometimes by function (gpio, net/mdio, spi), and sometimes under the generic mfd. I would like to start the upstream review process for our drivers, but first want to get recommendations on the source code layout. Is it permissible to keep a top level directory such as drivers/cisco to organize our code? It is not only the source code that is affected, but also provides a central place for Kconfig entries. Our FPGAs have multiple logical blocks, each of which is handled by a different MFD driver, e.g. i2c controllers, gpio controllers, spi controllers, mdio controllers. There can be multiple instances of each block as well (so multiple MFD devices are instantiated for each driver). And of course, there can be multiple FPGAs in a system, each with different combinations of logical blocks. The drivers themselves are pretty specific to our FPGAs, thus it makes sense to use Kconfig to select a hardware platform to automatically select the set of MFD drivers (and top level bus drivers) that would apply. Would a source layout putting all the code under drivers/cisco be acceptable in this case, or do I need to move things around and spread out the Kconfig entries across directories? I note that a single drivers/cisco would simplify any related modifications to MAINTAINERS as well.

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