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

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Date:   Fri, 15 Oct 2021 12:12:40 +0800
From:   Shawn Guo <shawnguo@...nel.org>
To:     Frieder Schrempf <frieder.schrempf@...tron.de>
Cc:     Frieder Schrempf <frieder@...s.de>, 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 Tue, Oct 05, 2021 at 07:17:13PM +0200, Frieder Schrempf wrote:
> 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.

Put all these good information into commit log, and I will be happy to
take it as a fix.

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
> >>