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

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Message-ID: <20250121092255.3108495-3-lukasz.czechowski@thaumatec.com>
Date: Tue, 21 Jan 2025 10:22:55 +0100
From: Lukasz Czechowski <lukasz.czechowski@...umatec.com>
To: 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
Cc: quentin.schulz@...rry.de,
	Lukasz Czechowski <lukasz.czechowski@...umatec.com>
Subject: [PATCH 2/2] arm64: dts: rockchip: Disable DMA for uart5 on px30-ringneck

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.

Signed-off-by: Lukasz Czechowski <lukasz.czechowski@...umatec.com>
---
 arch/arm64/boot/dts/rockchip/px30-ringneck.dtsi | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/boot/dts/rockchip/px30-ringneck.dtsi b/arch/arm64/boot/dts/rockchip/px30-ringneck.dtsi
index 2c87005c89bd3..e80412abec081 100644
--- a/arch/arm64/boot/dts/rockchip/px30-ringneck.dtsi
+++ b/arch/arm64/boot/dts/rockchip/px30-ringneck.dtsi
@@ -397,6 +397,8 @@ &u2phy_host {
 };

 &uart5 {
+	/delete-property/ dmas;
+	/delete-property/ dma-names;
 	pinctrl-0 = <&uart5_xfer>;
 };

-- 
2.43.0