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Date:   Tue, 18 Feb 2020 08:03:10 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc:     Schrempf Frieder <frieder.schrempf@...tron.de>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH 0/2] serial: imx: Backport fixes for irq handling to v4.14

On Tue, Feb 18, 2020 at 05:50:08AM +0100, gregkh@...uxfoundation.org wrote:
> On Mon, Feb 17, 2020 at 02:08:00PM +0000, Schrempf Frieder wrote:
> > From: Frieder Schrempf <frieder.schrempf@...tron.de>
> > 
> > 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
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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