linux-kernel - Re: [PATCH 5/8] arm64: dts: imx8mm-kontron: Fix CAN SPI clock frequency

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Date:   Tue, 5 Oct 2021 19:17:13 +0200
From:   Frieder Schrempf <frieder.schrempf@...tron.de>
To:     Shawn Guo <shawnguo@...nel.org>, Frieder Schrempf <frieder@...s.de>
Cc:     devicetree@...r.kernel.org, Krzysztof Kozlowski <krzk@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>, stable@...r.kernel.org,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>
Subject: Re: [PATCH 5/8] arm64: dts: imx8mm-kontron: Fix CAN SPI clock
 frequency

On 05.10.21 09:12, Shawn Guo wrote:
> On Thu, Sep 30, 2021 at 05:56:28PM +0200, Frieder Schrempf wrote:
>> From: Frieder Schrempf <frieder.schrempf@...tron.de>
>>
>> The MCP2515 can be used with an SPI clock of up to 10 MHz. Set the
>> limit accordingly to prevent any performance issues caused by the
>> really low clock speed of 100 kHz.
> 
> Could you share some testing result of this change?

Without this change, receiving CAN messages on the board beyond a
certain bitrate will cause overrun errors (see 'ip -det -stat link show
can0').

With this fix, receiving messages on the bus works without any overrun
errors for bitrates up to 1 MBit.


> 
>>
>> Fixes: 21c4f45b335f ("arm64: dts: Add the Kontron i.MX8M Mini SoMs and baseboards")
> 
> It's really an optimization rather than fix, isn't it?

It removes the arbitrarily low limit on the SPI frequency, that was
caused by a typo in the original dts. As the usage of the CAN bus is
seriously affected by this I would consider it a fix. But if you think
otherwise, feel free to remove the Fixes tag.

> 
> Shawn
> 
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Frieder Schrempf <frieder.schrempf@...tron.de>
>> ---
>>  arch/arm64/boot/dts/freescale/imx8mm-kontron-n801x-s.dts | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/boot/dts/freescale/imx8mm-kontron-n801x-s.dts b/arch/arm64/boot/dts/freescale/imx8mm-kontron-n801x-s.dts
>> index f2c8ccefd1bf..dbf11e03ecce 100644
>> --- a/arch/arm64/boot/dts/freescale/imx8mm-kontron-n801x-s.dts
>> +++ b/arch/arm64/boot/dts/freescale/imx8mm-kontron-n801x-s.dts
>> @@ -98,7 +98,7 @@ can0: can@0 {
>>  		clocks = <&osc_can>;
>>  		interrupt-parent = <&gpio4>;
>>  		interrupts = <28 IRQ_TYPE_EDGE_FALLING>;
>> -		spi-max-frequency = <100000>;
>> +		spi-max-frequency = <10000000>;
>>  		vdd-supply = <&reg_vdd_3v3>;
>>  		xceiver-supply = <&reg_vdd_5v>;
>>  	};
>> -- 
>> 2.33.0
>>