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 09:44:46 +0000
From:   Schrempf Frieder <frieder.schrempf@...tron.de>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
CC:     "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 18.02.20 08:17, gregkh@...uxfoundation.org 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@...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
> 
> 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