May 2024 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

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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