netdev - Re: [PATCH v10 0/2] Enable multiple MCAN on AM62x

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Date: Mon, 10 Jul 2023 11:57:51 +0200
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Judith Mendez <jm@...com>
Cc: Chandrasekar Ramakrishnan <rcsekar@...sung.com>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	"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>,
	Tero Kristo <kristo@...nel.org>, Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	devicetree@...r.kernel.org,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Simon Horman <simon.horman@...igine.com>
Subject: Re: [PATCH v10 0/2] Enable multiple MCAN on AM62x

On 07.07.2023 15:47:12, Judith Mendez wrote:
> On AM62x there are two MCANs 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 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.
> 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.

Latency

> 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

However

> 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.
> 
> v9:
> Link: https://lore.kernel.org/linux-can/20230419223323.20384-1-jm@ti.com/T/#t
> 
> v8:
> Link: https://lore.kernel.org/linux-can/20230530224820.303619-1-jm@ti.com/T/#t
> 
> v7:
> Link: https://lore.kernel.org/linux-can/20230523023749.4526-1-jm@ti.com/T/#t
> 
> v6:
> Link: https://lore.kernel.org/linux-can/20230518193613.15185-1-jm@ti.com/T/#t
> 
> v5:
> Link: https://lore.kernel.org/linux-can/20230510202952.27111-1-jm@ti.com/T/#t
> 
> v4:
> Link: https://lore.kernel.org/linux-can/c3395692-7dbf-19b2-bd3f-31ba86fa4ac9@linaro.org/T/#t

The link doesn't point to v4, fixed.

> 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

Was there a v1? That link doesn't point to it, removed.

> 
> RFC:
> Link: https://lore.kernel.org/linux-can/52a37e51-4143-9017-42ee-8d17c67028e3@ti.com/T/#t

Doesn't point to RFC, fixed.

Applied to linux-can-next/testing.

Thanks,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
Vertretung Nürnberg              | Phone: +49-5121-206917-129 |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-9   |

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