Showing posts with label linux kernel. Show all posts
Showing posts with label linux kernel. Show all posts

Saturday, 24 August 2013

Discovered problems in Linux kernel connections to USB devices

Because of a faulty coordination between the hardware and the USB stack in the energy management of the Linux kernel connections to USB devices are frequently interrupted. So far, the kernel developers have looked to blame the device manufacturers. The kernel hacker Sarah Sharp has discovered a serious bug in the Linux kernel. Thus, a faulty coordination between USB stack and equipment when leaving the sleep mode is responsible for the connection to USB devices are abruptly cut off when auto-suspend is enabled. A patch is in the works. The problem of indiscriminate terminations of connections to USB devices is there and other kernel hackers known for years, writes Sharp. However, they have "cheap, crappy and broken" to blame searched devices, so the manufacturers. The blacklists created for this purpose by the kernel developers have become too big someday. The white lists created later by the individual distributions were insufficiently maintained, and ultimately costly. Now, according to Sharp; it is turned out , that the devices were not always responsible for the disruption. According to USB specifications of roothub must send at least 20 milliseconds, the signal to wake up a device (TDRSMDN). Then the status of a device is placed in the hub to Active. Have access to the Linux kernel and software on a device that has yet to be made a break of 10 milliseconds (TRSMRCY). The TRSMRCY value is defined by the USB 2.0 specification, however, neither a read nor a maximum, but a minimum value. Although the xHCI driver of the Linux kernel, the kernel activates immediately hub daemon (khubd), is the changing status of a device, but only after 20 ms free (TDRSMDN). This means that a device can be longer in a Resume mode than that specified in TRSMRCY time. The software then attempts to 10 milliseconds to access the device, although it is still in sleep mode, which in turn can cause the USB device is disconnected or, for example, writes cannot be done. The error relates to devices that connect to the xHCI hub. Such problems with the EHCI hub and the USB stack of the Linux kernel does not exist. After Sharp's first analyzes some USB devices have a TRSMRCY-time of up to 17 milliseconds. 8 percent of the tested devices TRSMRCY-values are about 10 milliseconds. A first patch Sharp has already submitted. But it was still not a "real fix". Immediately they work on a better patch. But you see "light at the end of the tunnel" and that the problems would be resolved with the USB power management in the Linux kernel soon. If everything goes according to plan, the repairs should already be included in the next kernel version 3.11, which should appear early September 2013.

Monday, 29 April 2013

The Linux kernel version 3.9 available!

Open Source Announced Version 3.9 of the Linux kernel and was released last night on the website announced by its founder, Linus Torvalds, in the developer mailing list. This publication comes ten weeks after the previous version, and have continuity in support for new hardware. "Whatever the reason, this week has been very quiet, which makes me more comfortable to publish the final version 3.9, so I think the last-rc8 has stopped working," announced on Mailing List founder of the Linux kernel. No big change announced for this version, but a deepening of transitions already Commencement with version 3.8. Here is a non-exhaustive selection. As usual, for a comprehensive overview of the latest news and management visit: Improved support for ARM architectures is supported. Begun in version 3.7, it now allows the teams to the Linux Foundation announce support for 18 SoC (system on a chip) ARM. The goal, says, is to arrive at a single core for all platforms, including x86. Better implementation of the standard IPv6 network. Improvements were made especially in terms of security when encapsulating IPv6 inside IPv4. It supports distribution systems RAID 5 and RAID 6 system BTRFS files. And extension compatibility for graphics drivers, including future Haswell and Valley View and Oland AMD chips were added. Improved supported virtualization, with extension to ARM Cortex A15 chips in KVM and Xen supported by the summer. We wish to pass an interesting point in the statistics of this version 3.9. If they are, as usual, the opportunity to highlight the most active developers, they also show a significant change on the part of companies that support the Linux kernel participating. Thus, for the first time, is for Intel one of the top ranking contributing companies.