https://bugzilla.kernel.org/show_bug.cgi?id=201753 --- Comment #20 from David Coe (david.coe@xxxxxxxxxx) --- More results and some progress!! A. Alex Hung (Ubuntu) has cherry-picked the kernel-commit [1} of Suravee's version 3 patch and placed test-builds on [2]. It works for his Ryzen 2500U. Bravo for a quick take-up! I've checked it out and (alas, as expected with the original 5 x 20 msec delay) it is isn't enough for my Ryzen 2400G which needs ~120 msecs to respond :-(. B. I've done a couple more rebuilds for the current kernels on Ubuntu 20.10 and 21.04 using Suravee's patch updated both with Pauls' retry-logging and with increasing the maximum delay to 25 x 20 msec. Grepp'ing dmesg for IOMMU (on my 2400g) gives: [ 1.018329] pci 0000:00:00.2: AMD-Vi: IOMMU performance counters supported (retry = 19) [ 1.022185] pci 0000:00:00.2: AMD-Vi: Found IOMMU cap 0x40 [ 1.023669] perf/amd_iommu: Detected AMD IOMMU #0 (2 banks, 4 counters/bank). [ 1.283218] AMD-Vi: AMD IOMMUv2 driver by Joerg Roedel <jroedel@xxxxxxx> The retrys count backwards so that confirms the Ryzen 2500G still needs 120 msecs to respond. My (very strong) proposal is that we increase Suravee's retry-count to something large enough to cover the numerous entry-level Ryzen's out there. Only the absolutely necessary boot-up delay is introduced (and checked, if required, by Paul's logging statement). Most purchasers of Ryzen CPUs are then covered! Only the dyed-in-the-wool speed-merchants have to make a choice between boot-up time and IOMMU capability - at least until the underlying problem can be corrected in firmware or silicon. Thanks again, good people. David [1]. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6778ff5b21bd8e78c8bd547fd66437cf2657fd9b [2]. https://people.canonical.com/~alexhung/LP1917203/ -- You may reply to this email to add a comment. You are receiving this mail because: You are watching the assignee of the bug.
