On 7.1.2025 16.35, Michal Pecio wrote:
Raspberry Pi is a major user of those chips and they discovered a bug - when the end of a transfer ring segment is reached, up to four TRBs can be prefetched from the next page even if the segment ends with link TRB and on page boundary (the chip claims to support standard 4KB pages). It also appears that if the prefetched TRBs belong to a different ring whose doorbell is later rung, they may be used without refreshing from system RAM and the endpoint will stay idle if their cycle bit is stale. Other users complain about IOMMU faults on x86 systems, unsurprisingly. Deal with it by using existing quirk which allocates a dummy page after each transfer ring segment. This was seen to resolve both problems. RPi came up with a more efficient solution, shortening each segment by four TRBs, but it complicated the driver and they ditched it for this quirk. Also rename the quirk and add VL805 device ID macro. Signed-off-by: Michal Pecio <michal.pecio@xxxxxxxxx> Link: https://github.com/raspberrypi/linux/issues/4685 Closes: https://bugzilla.kernel.org/show_bug.cgi?id=215906 CC: stable@xxxxxxxxxxxxxxx
Thanks, adding to queue -Mathias
