linux-kernel - Re: [PATCH v4 0/4] Enable multiple MCAN on AM62x

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Message-ID: <c3395692-7dbf-19b2-bd3f-31ba86fa4ac9@linaro.org>
Date:   Tue, 2 May 2023 08:52:27 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Judith Mendez <jm@...com>,
        Chandrasekar Ramakrishnan <rcsekar@...sung.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Schuyler Patton <spatton@...com>, Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Tero Kristo <kristo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Simon Horman <simon.horman@...igine.com>
Subject: Re: [PATCH v4 0/4] Enable multiple MCAN on AM62x

On 02/05/2023 00:46, Judith Mendez wrote:
> On AM62x there is one MCAN in MAIN domain and two in MCU domain.
> The MCANs in MCU domain were not enabled since there is no
> hardware interrupt routed to A53 GIC interrupt controller.
> Therefore A53 Linux cannot be interrupted by MCU MCANs.
> 
> This solution instantiates a hrtimer with 1 ms polling interval
> for MCAN device when there is no hardware interrupt and there is
> poll-interval property in DTB MCAN node. The hrtimer generates a
> recurring software interrupt which allows to call the isr. The isr
> will check if there is pending transaction by reading a register
> and proceed normally if there is.
> 
> On AM62x, this series enables two MCU MCAN which will use the hrtimer
> implementation. MCANs with hardware interrupt routed to A53 Linux
> will continue to use the hardware interrupt as expected.
> 
> Timer polling method was tested on both classic CAN and CAN-FD
> at 125 KBPS, 250 KBPS, 1 MBPS and 2.5 MBPS with 4 MBPS bitrate
> switching.
> 
> Letency and CPU load benchmarks were tested on 3x MCAN on AM62x.
> 1 MBPS timer polling interval is the better timer polling interval
> since it has comparable latency to hardware interrupt with the worse
> case being 1ms + CAN frame propagation time and CPU load is not
> substantial. Latency can be improved further with less than 1 ms
> polling intervals, howerver it is at the cost of CPU usage since CPU
> load increases at 0.5 ms.
> 
> Note that in terms of power, enabling MCU MCANs with timer-polling
> implementation might have negative impact since we will have to wake
> up every 1 ms whether there are CAN packets pending in the RX FIFO or
> not. This might prevent the CPU from entering into deeper idle states
> for extended periods of time.
> 
> This patch series depends on 'Enable CAN PHY transceiver driver':
> Link: https://lore.kernel.org/lkml/775ec9ce-7668-429c-a977-6c8995968d6e@app.fastmail.com/T/
> 
> v2:
> Link: https://lore.kernel.org/linux-can/20230424195402.516-1-jm@ti.com/T/#t
> 
> V1:
> Link: https://lore.kernel.org/linux-can/19d8ae7f-7b74-a869-a818-93b74d106709@ti.com/T/#t
> 
> RFC:
> Link: https://lore.kernel.org/linux-can/52a37e51-4143-9017-42ee-8d17c67028e3@ti.com/T/#t
> 
> Changes since v3:
> - Wrong patch sent, resend correct patch series

Sending patchsets every 10 minutes does not help us...

Best regards,
Krzysztof