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

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Date:   Tue, 18 Feb 2020 05:50:08 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Schrempf Frieder <frieder.schrempf@...tron.de>
Cc:     "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.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 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.

greg k-h