[PATCH] dts: Disable DMA support on the BK4 vf610 device's fsl_lpuart driver

[PATCH] dts: Disable DMA support on the BK4 vf610 device's fsl_lpuart driver

[Lukasz Majewski]

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@denx.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 = "","";
 	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";
 };
 
-- 
2.20.1

Re: [PATCH] dts: Disable DMA support on the BK4 vf610 device's fsl_lpuart driver

[Robin Murphy]

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@denx.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";
>   };
>   
> 

Re: [PATCH] dts: Disable DMA support on the BK4 vf610 device's fsl_lpuart driver

[Lukasz Majewski]

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Hi Robin,

> 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@denx.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;"?

I don't want to strip the dma-names property globally. I just want to
adjust this particular driver mode from DMA to PIO.

For my use cases - as written in the commit message - the PIO mode is
more suitable (and reliable). 

> 
> 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";
> >   };
> >   
> >   




Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de

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Re: [PATCH] dts: Disable DMA support on the BK4 vf610 device's fsl_lpuart driver

[Robin Murphy]

On 09/10/2019 15:44, Lukasz Majewski wrote:
> Hi Robin,
> 
>> 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@denx.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;"?
> 
> I don't want to strip the dma-names property globally. I just want to
> adjust this particular driver mode from DMA to PIO.

What do you mean by "globally"? The /delete-property/ operator just 
removes a previously-defined property from the node in which it appears.
> For my use cases - as written in the commit message - the PIO mode is
> more suitable (and reliable).

Right, and having invalid "dma-names" properties for this board is what 
happens to trick Linux into not using DMA mode via 
of_dma_request_slave_channel() failing, yes? What I'm saying is that if 
the underlying justification is that it's not worth using DMA mode at 
all on this board, then suppressing the actual "dmas" property it its 
DTS such that there's no dependency on a particular driver behaviour is 
a lot more robust.

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";
>>>    };
>>>    
>>>    
> 
> 
> 
> 
> Best regards,
> 
> Lukasz Majewski
> 
> --
> 
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de
>