linux-kernel - Re: [PATCH] dts: Disable DMA support on the BK4 vf610 device's fsl

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Date:   Wed, 9 Oct 2019 15:40:00 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Lukasz Majewski <lukma@...x.de>, linux-kernel@...r.kernel.org,
        Shawn Guo <shawnguo@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Stefan Agner <stefan@...er.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] dts: Disable DMA support on the BK4 vf610 device's
 fsl_lpuart driver

On 09/10/2019 15:30, Lukasz Majewski wrote:
> This change disables the DMA support (RX/TX) on the NXP's fsl_lpuart
> driver - the PIO mode is used instead. This change is necessary for better
> robustness of BK4's device use cases with many potentially interrupted
> short serial transfers.
> 
> Without it the driver hangs when some distortion happens on UART lines.
> 
> Signed-off-by: Lukasz Majewski <lukma@...x.de>
> ---
>   arch/arm/boot/dts/vf610-bk4.dts | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm/boot/dts/vf610-bk4.dts b/arch/arm/boot/dts/vf610-bk4.dts
> index 0f3870d3b099..ad20f3442d40 100644
> --- a/arch/arm/boot/dts/vf610-bk4.dts
> +++ b/arch/arm/boot/dts/vf610-bk4.dts
> @@ -259,24 +259,28 @@
>   &uart0 {
>   	pinctrl-names = "default";
>   	pinctrl-0 = <&pinctrl_uart0>;
> +	dma-names = "","";

This looks like a horrible hack - is there any reason not to just strip 
things at compile-time, i.e. "/delete-property/ dmas;"?

Robin.

>   	status = "okay";
>   };
>   
>   &uart1 {
>   	pinctrl-names = "default";
>   	pinctrl-0 = <&pinctrl_uart1>;
> +	dma-names = "","";
>   	status = "okay";
>   };
>   
>   &uart2 {
>   	pinctrl-names = "default";
>   	pinctrl-0 = <&pinctrl_uart2>;
> +	dma-names = "","";
>   	status = "okay";
>   };
>   
>   &uart3 {
>   	pinctrl-names = "default";
>   	pinctrl-0 = <&pinctrl_uart3>;
> +	dma-names = "","";
>   	status = "okay";
>   };
>   
>