linux-kernel - Re: [PATCH v3 0/4] Enable multiple MCAN on AM62x

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Message-ID: <5ec79304-0339-517a-a5e6-92054eec2d2e@ti.com>
Date:   Mon, 1 May 2023 18:20:54 -0500
From:   Judith Mendez <jm@...com>
To:     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 v3 0/4] Enable multiple MCAN on AM62x

Hello all,

On 5/1/23 17:31, 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 v2:
> - Change binding patch first
> - Update binding poll-interval description
> - Add oneOf to select either interrupts/interrupt-names or poll-interval
> - Sort list of includes
> - Create a define for 1 ms polling interval
> - Change plarform_get_irq to optional to not print error msg
> - Fix indentations, lengths of code lines, and added other style changes
> 
> Changes since v1:
> - Add poll-interval property to bindings and MCAN DTB node
> - Add functionality to check for 'poll-interval' property in MCAN node 
> - Bindings: add an example using poll-interval
> - Add 'polling' flag in driver to check if device is using polling method
> - Check for both timer polling and hardware interrupt case, default to
> hardware interrupt method
> - Change ns_to_ktime() to ms_to_ktime()

Please ignore this version v3, apologies for sending the wrong patches.

regards,
Judith