Pci hot reset

12.03.2021

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Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. By this I mean I would like to be able to:. If so is there any good resources for how to use the Hotplug system with PCIe? LDD does not quite cover it thoroughly enough.

We are using it the same way as you described it. The driver xillybus is not unloaded, just disconnected. A better solution is to rescan only the node where your FPGA is attached to. This reduces the over all impact for the system.

Here is how to reset the Vegas before same as a reset in windows. This is based on the Vendor ID. This is really dependent on exactly what is changed on the FPGA. The problem is in how PCIe enumeration and address assignment is done, particularly how the PCIe switches are configured.

The allocation MUST be done in one shot as a depth-first search. After this is complete, it is not possible to go insert additional bus numbers or address space without changing all of the subsequent allocations, which would require reloading all of the corresponding device drivers.

Basically, once the bus is enumerated and addresses are assigned, you can't change the overall allocations without re-enumerating the entire bus, which requires a reboot. If the BAR configuration has changed, then it's a different story. If the new BARs are smaller, then there should be no problem. But if the new BARs are larger or there are more BARs, if there isn't enough address space allocated to the switch port that the device is attached to, then those BARs cannot be allocated address space and the device will fail to enumerate.

In this case, a reboot is required to so that resources can be reassigned. If you're going from no device to a device i. Learn more. Asked 5 years, 1 month ago. Active 2 days ago. Viewed 62k times. Look at PCIe hotplug mechanism. It's supported in newer kernels. Actually how by your opinion Thunderbolt will work? It's the same here. Are you executing rescan on the host machine or inside a Xen VM?

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Xen had problem to rescan the PCIe tree and crashed in the past. I don't know if it is solved. I'm wondering what base hardware are you using. In my experience with commercial grade motherboards the rescan method rarely worked.

I went the partial reconfiguration route to solve the problem by not reenumerating. Paebbels whh can you share your setup? To my knowledge, its independent of the hardware. If a system supports rescaning is a matter of kernel software and support for the particular platform root complex driver,Help answer threads with 0 replies. Welcome to LinuxQuestions. You are currently viewing LQ as a guest.

PCI Express System Architecture by Tom Shanley, Don Anderson, Ravi Budruk, MindShare, Inc

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Having a problem logging in? Please visit this page to clear all LQ-related cookies. Introduction to Linux - A Hands on Guide This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter.

For more advanced trainees it can be a desktop reference, and a collection of the base knowledge needed to proceed with system and network administration. This book contains many real life examples derived from the author's experience as a Linux system and network administrator, trainer and consultant. They hope these examples will help you to get a better understanding of the Linux system and that you feel encouraged to try out things on your own.

Click Here to receive this Complete Guide absolutely free. I have a PCI device that is sitting behind a bridge. Under certain circumstances the PCI device will become inactive. The bridge appears to still be functional. I am trying to figure out how to bring the device back online. I tried toggling the secondary bus reset bit of the Bridge Control Register but it doesn't appear to make any difference.

Given that these two methods are not helping me out what other choices do I have to either reset the PCI device or hot-plug the device from a kernel driver. Or some other method of bring the device back to life. Note that I am running Linux 4. Thanks, Kelly. Having any form of virtualization in your path adds the question: "Is it the hardware or the virtualization screwing up? Try the hardware without the virtualization and see if life improves.

Find More Posts by cyent. Hardware is sometimes timing sensitive, so adding in a bunch of cycles delay through virtualization can cause sorrow. Sometimes rmmod'ing the driver and then modprobe'ing it works to revive sad hardware. If you can't rmmod it, you may have to remove the entire stack of mods that depends on it first.

I tried rmmod but it hard hung the system. Thinking back however my driver assumes that the device is still active when it does an rmmod. During rmmod it tries to "uninitialized" the device. Touching the hardware hung the system.In other words, this allows safe [2]non-privileged, userspace drivers.

Why do we want that? From a device and host perspective, this simply turns the VM into a userspace driver, with the benefits of significantly reduced latency, higher bandwidth, and direct use of bare-metal device drivers [3]. Some applications, particularly in the high performance computing field, also benefit from low-overhead, direct device access from userspace.

Prior to VFIO, these drivers had to either go through the full development cycle to become proper upstream driver, be maintained out of tree, or make use of the UIO framework, which has no notion of IOMMU protection, limited interrupt support, and requires root privileges to access things like PCI configuration space.

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Without going into the details of each of these, DMA is by far the most critical aspect for maintaining a secure environment as allowing a device read-write access to system memory imposes the greatest risk to the overall system integrity. To help mitigate this risk, many modern IOMMUs now incorporate isolation properties into what was, in many cases, an interface only meant for translation ie.

With this, devices can now be isolated from each other and from arbitrary memory access, thus allowing things like secure direct assignment of devices into virtual machines.

This isolation is not always at the granularity of a single device though. For instance, an individual device may be part of a larger multi- function enclosure. Topology can also play a factor in terms of hiding devices.

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Therefore, while for the most part an IOMMU may have device level granularity, any system is susceptible to reduced granularity. A group is a set of devices which is isolatable from all other devices in the system. Groups are therefore the unit of ownership used by VFIO. In IOMMUs which make use of page tables, it may be possible to share a set of page tables between different groups, reducing the overhead both to the platform reduced TLB thrashing, reduced duplicate page tablesand to the user programming only a single set of translations.

For this reason, VFIO makes use of a container class, which may hold one or more groups. On its own, the container provides little functionality, with all but a couple version and extension query interfaces locked away. The user needs to add a group into the container for the next level of functionality.

To do this, the user first needs to identify the group associated with the desired device. This can be done using the sysfs links described in the example below. If a group fails to set to a container with existing groups, a new empty container will need to be used instead. Additionally, it now becomes possible to get file descriptors for each device within a group using an ioctl on the VFIO group file descriptor. This device is on the pci bus, therefore the user will make use of vfio-pci to manage the group:.

Binding this device to the vfio-pci driver creates the VFIO group character devices for this group:. Device e. The user now has full access to all the devices and the iommu for this group and can access them as follows:. The driver provides an ops structure for callbacks similar to a file operations structure:. This allows the bus driver an easy place to store its opaque, private data.

PPC64 guests are paravirtualized but not fully emulated. The locked pages accounting is done at this point. This lets user first to know what the DMA window is and adjust rlimit before doing any real job. The platform has to support the functionality or error will be returned to the userspace.

It creates a new window in the available slot and returns the bus address where the new window starts. Due to hardware limitation, the user space cannot choose the location of DMA windows. In this case the device is below a PCI bridge, so transactions from either function of the device are indistinguishable to the iommu:.

The Linux Kernel 5.Resets in PCI express are a bit complex. There are two main types of resets - conventional reset, and function-level reset. There are also two types of conventional resets, fundamental resets and non-fundamental resets. See the PCI express specification for all of the details. A 'cold reset' is a fundamental reset that takes place after power is applied to a PCIe device. There appears to be no standard way of triggering a cold reset, save for turning the system off and back on again.

A 'warm reset' is a fundamental reset that is triggered without disconnecting power from the device. There appears to be no standard way of triggering a warm reset.

pci hot reset

A 'hot reset' is a conventional reset that is triggered across a PCI express link. A hot reset is triggered either when a link is forced into electrical idle or by sending TS1 and TS2 ordered sets with the hot reset bit set. Software can initiate a hot reset by setting and then clearing the secondary bus reset bit in the bridge control register in the PCI configuration space of the bridge port upstream of the device.

It must not reset the entire PCIe device. Implementing function-level resets is not required by the PCIe specification. A function-level reset is initiated by setting the initiate function-level reset bit in the function's device control register in the PCI express capability structure in the PCI configuration space. Writing a 1 to this file will initiate a function-level reset on the corresponding function.

Note that this only affects that specific function of the device, not the whole device, and devices are not required to implement function-level resets as per the PCIe specification.

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I am not aware of any 'nice' method for triggering a hot reset there is no sysfs entry for that. However, it is possible to use setpci to do so with the following script:. Ensure that all attached drivers are unloaded before running this script. This script will attempt to remove the PCIe device, then command the upstream switch port to issue a hot reset, then attempt to rescan the PCIe bus. This script has also only been tested on devices with a single function, so it may need some reworking for devices with multiple functions.The free OSR Learning Library has more than 50 articles on a wide variety of topics about writing and debugging device drivers and Minifilters.

From introductory level to advanced. All the articles have been recently reviewed and updated, and are written using the clear and definitive style you've come to expect from OSR over the years. It looks like you're new here. If you want to get involved, click one of these buttons! I would like to have a function that is hardware reset the device.

The device driver is unloaded automatically by the Windows now. After finishing reset process, the hardware will link to the PCI-E. How should I do that the driver will be loaded automatically without any manual rescan. I mean that I hope the application will not be aware of this reset action and the application can continue executing. April I'm not sure if this is what you want but I manage a similar thing on one of my drivers.

pci hot reset

Obviously this can't be done while I'm still connected to it so I issue a command to the hardware that tells it to re-start when it receives a power-down instruction.

Then I unload the driver which, when it is finished sends the power-down PCIe command and the device re-boots. I wait a suitable length of time for the device to return and reload the driver and it all works. The views stated herein do not necessarily represent the view of the company. If you are not the intended recipient of this Email you may not copy, forward, disclose or otherwise use it or any part of it in any form whatsoever.

If you have received this mail in error please Email the sender. If your BIOS doesn't support that, then your device will never be unloaded, because no one will ever report that you have gone missing. In that case, you have a bit of a problem, because your board will not get its PCI configuration space rewritten after it comes back from reset. However, even in this case, your application must be involved in the process.

Its open handle will be invalidated when the board goes away. The driver cannot fully unload until the application closes its handle. It has to open a new handle to get the new driver. You can use the plug-and-play notifications to find out about these events. You can hide most of this in a DLL so that application remains relatively ignorant.

Personally, it seems to me that this level of reset is just a bad idea.

pci hot reset

It's always good to have a board-level reset, but that reset should always keep the PCIe link alive. Hi Graeme: Thanks for your reply! I think my system is like to yours. Is your driver loaded or unloaded automatically? Or is any function call to do this? Would you tell me how to achieve this goal? Thanks for your reply! No problem Felix, I've had enough help over the years from this forum it's nice to give something back for a change.Welcome to the most active Linux Forum on the web.

Welcome to LinuxQuestions. You are currently viewing LQ as a guest. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features. Registration is quick, simple and absolutely free. Join our community today! Note that registered members see fewer ads, and ContentLink is completely disabled once you log in. Are you new to LinuxQuestions. If you need to reset your password, click here.

Having a problem logging in? Please visit this page to clear all LQ-related cookies. Introduction to Linux - A Hands on Guide This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter.

For more advanced trainees it can be a desktop reference, and a collection of the base knowledge needed to proceed with system and network administration.

This book contains many real life examples derived from the author's experience as a Linux system and network administrator, trainer and consultant. They hope these examples will help you to get a better understanding of the Linux system and that you feel encouraged to try out things on your own.

Click Here to receive this Complete Guide absolutely free. First if this belongs in hardware or somewhere else forgive me. My book says that hot reset is a software function. I really need to learn what string of commands to use to issue and recover from a hot reset on the PCIe bus. My device is connected via a cable and I am running Centos 6. I can see my device just fine the question is really about being able to do the hot reset on a particular slot.Typically, a reconnection mechanism is also offered, so that the affected PCI device s are reset and put back into working condition.

The reset phase requires coordination between the affected device drivers and the PCI controller chip. This document describes a generic API for notifying device drivers of a bus disconnection, and then performing error recovery.

This API is currently implemented in the 2. Reporting and recovery is performed in several steps. First, when a PCI hardware error has resulted in a bus disconnect, that event is reported as soon as possible to all affected device drivers, including multiple instances of a device driver on multi-function cards.

Next, recovery is performed in several stages. Most of the complexity is forced by the need to handle multi-function devices, that is, devices that have multiple device drivers associated with them. The biggest reason for choosing a kernel-based implementation rather than a user-space implementation was the need to deal with bus disconnects of PCI devices attached to storage media, and, in particular, disconnects from devices holding the root file system.

PCI Hot Swap Controllers

If the root file system is disconnected, a user-space mechanism would have to go through a large number of contortions to complete recovery. By contrast, bus errors are easy to manage in the device driver. Design and implementation details below, based on a chain of public email discussions with Ben Herrenschmidt, circa 5 April If a callback is not implemented, the corresponding feature is considered unsupported.

The actual steps taken by a platform to recover from a PCI error event will be platform-dependent, but will follow the general sequence described below. At this point, the device might not be accessible anymore, depending on the platform the slot will be isolated on powerpc. Called in task context. See note about interrupts at the end of this doc. All drivers participating in this system must implement this call.

The driver must return one of the following result codes:.

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Doing better requires complex multi-threaded logic in the error recovery implementation e. This seems excessively complex and not worth implementing. A reboot is then required to get the device working again. IOs are allowed again, but DMA is not, with some restrictions. This callback is made if all drivers on a segment agree that they can try to recover and if no automatic link reset was performed by the HW. However, such an error might cause IOs to be re-blocked for the whole segment, and thus invalidate the recovery that other devices on the same segment might have done, forcing the whole segment into one of the next states, that is, link reset or slot reset.

The next step taken depends on the results returned by the drivers. The platform resets the link. The actual steps taken by a platform to perform a slot reset will be platform-dependent.

Powerpc platforms implement two levels of slot reset: soft reset default and fundamental optional reset. Soft reset is also known as hot-reset. For most PCI devices, a soft reset will be sufficient for recovery. Optional fundamental reset is provided to support a limited number of PCI Express devices for which a soft reset is not sufficient for recovery.

After a slot reset, the device driver will almost always use its standard device initialization routines, and an unusual config space setup may result in hung devices, kernel panics, or silent data corruption.

This call gives drivers the chance to re-initialize the hardware re-download firmware, etc. At this point, the driver may assume that the card is in a fresh state and is fully functional. For example, the Symbios sym53cxx2 driver performs device init only from PCI function However, it probably should. The goal of this callback is to tell the driver to restart activity, that everything is back and running. This callback does not return a result code. The device driver should, at this point, assume the worst.

pci hot reset