linux-kernel - Re: [PATCH 2/2] arm64: dts: rockchip: Disable DMA for uart5 on px30-ringneck

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Message-ID: <2be46f44-6c81-417b-b0b9-7325cb0f7c10@cherry.de>
Date: Tue, 21 Jan 2025 10:41:42 +0100
From: Quentin Schulz <quentin.schulz@...rry.de>
To: Lukasz Czechowski <lukasz.czechowski@...umatec.com>,
 linux-arm-kernel@...ts.infradead.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, heiko@...ech.de, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: dts: rockchip: Disable DMA for uart5 on
 px30-ringneck

Hi Lukasz,

On 1/21/25 10:22 AM, Lukasz Czechowski wrote:
> UART controllers without flow control seem to behave unstable
> in case DMA is enabled. The issues were indicated in the message:
> https://lore.kernel.org/linux-arm-kernel/CAMdYzYpXtMocCtCpZLU_xuWmOp2Ja_v0Aj0e6YFNRA-yV7u14g@mail.gmail.com/
> In case of PX30-uQ7 Ringneck SoM, it was noticed that after couple
> of hours of UART communication, the CPU stall was occurring,
> leading to the system becoming unresponsive.
> After disabling the DMA, extensive UART communication tests for
> up to two weeks were performed, and no issues were further
> observed.
> The flow control pins for uart5 are not available on PX30-uQ7
> Ringneck, as configured by pinctrl-0, so the DMA nodes were
> removed on SoM dtsi.
> 

Reviewed-by: Quentin Schulz <quentin.schulz@...rry.de>

We should backport this to stable releases too, so please follow the 
instructions from here: 
https://www.kernel.org/doc/html/latest/process/submitting-patches.html#select-the-recipients-for-your-patch

Essentially:

Cc: stable@...r.kernel.org

in the commit log and we'll need a

Fixes: <commit hash>

trailer as well with the commit hash of the commit introducing the issue 
(likely the one defining uart5 for Ringneck for us).

Considering that UART0 CTS and RTS are routed to Q7 header but only 
usable when Haikou exposes UART0 on the DB9 connector (via the SW2 
switch), which is NOT the default state (and in any case not supported 
by our current device tree), I believe we should make the same change to 
the uart0 node in haikou dts for Ringneck. What do you think? Can you 
send another patch for that one?

Thanks!
Quentin