Ryzen CPU bug crashes PCs using Firewire devices — old school interface causes new school problems on Linux PCs

A Linux patch is on the way to solve crashing issues when attempting to use Firewire devices on PCs running Ryzen CPUs and Linux (via Phoronix). The unlikely hardware combination has enough Linux users to get attention from the community, and even a fix coming out with Linux 6.7 will be backported to prior Linux kernel releases.

Firewire, or IEEE 1394, is a data interface designed in the 1980s and most commonly found on Apple Mac computers and digital video cameras. It had many advantages over USB, which came out a decade later but ultimately failed to gain much attraction outside the audio-video market. Steve Jobs pronounced Firewire dead in 2008, and Thunderbolt practically replaced it in 2011.

Despite all that, Linux developer Takashi Sakamoto has pledged to keep Firewire support on Linux alive until 2029. Sakamoto is already making good on his promise with his latest patch, which solves an issue that uniquely affected PCs running AMD Ryzen CPUs. It would seem incredibly unlikely that anyone would be combining two pieces of hardware with nearly a decade between them, but those people certainly exist. They reported an unusually high amount of crashes.

Without getting too technical, Firewire and Ryzen users would often see their PCs crash if the “isochronous cycle timer” register on the CPU was accessed. This register would be accessed if a user ever plugged in a Firewire device or was using software that required constant access to the register.

To fix the bug, Sakamoto’s patch doesn’t allow access to the register, preventing crashing and time-aware software from being used. In that sense, it’s not a complete fix but more of a workaround. This patch will arrive in Linux 6.7 (which launches tomorrow) and will be retroactively applied to older kernels that are still maintained and supported.

Although crashes are no longer a problem for Firewire-Ryzen PCs, the patch is a double-edged sword and “brings apparent disadvantage since time-aware application programs require it,” according to Sakamoto. Linux users with this hardware combination might have to switch to Intel or even downgrade to one of AMD’s pre-Ryzen CPUs, as neither exhibit the same problems seen on Ryzen-powered PCs.

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