On 18.02.20 08:17, gregkh@xxxxxxxxxxxxxxxxxxx wrote: > On Tue, Feb 18, 2020 at 08:03:10AM +0100, Uwe Kleine-König wrote: >> On Tue, Feb 18, 2020 at 05:50:08AM +0100, gregkh@xxxxxxxxxxxxxxxxxxx wrote: >>> On Mon, Feb 17, 2020 at 02:08:00PM +0000, Schrempf Frieder wrote: >>>> From: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx> >>>> >>>> A customer of ours has problems with RS485 on i.MX6UL with the latest v4.14 >>>> kernel. They get an exception like below from time to time (the trace is >>>> from an older kernel, but the problem also exists in v4.14.170). >>>> >>>> As the cpuidle state 2 causes large delays for the interrupt that controls the >>>> RS485 RTS signal (which can lead to collisions on the bus), cpuidle state 2 was >>>> disabled on this system. This aspect might cause the exception happening more >>>> often on this system than on other systems with default cpuidle settings. >>>> >>>> Looking for solutions I found Uwe's patches that were applied in v4.17 being >>>> mentioned here [1] and here [2]. In [1] Uwe notes that backporting these fixes >>>> to v4.14 might not be trivial, but I tried and in my opinion found it not to be >>>> too problematic either. >>>> >>>> With the backported patches applied, our customer reports that the exceptions >>>> stopped occuring. Given this and the fact that the problem seems to be known >>>> and quite common, it would be nice to get this into the v4.14 stable tree. >>> >>> Thanks for the backports, both now queued up. >> >> To complete these fixes you also want to backport >> >> 101aa46bd221 serial: imx: fix a race condition in receive path > > If so, it needs to also go to 4.19.y, and someone needs to provide a > working backport for both places :) I can try to come up with something. But I don't have a system that is affected by this (only single core) to test. Best regards, Frieder
