Re: [PATCH 0/2] serial: imx: Backport fixes for irq handling to v4.14

From: Uwe Kleine-König
Date: Tue Feb 18 2020 - 02:03:23 EST

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

Best regards

Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | |