linux-kernel - Re: [PATCH 04/15] can: m_can: Use transmit event FIFO watermark level interrupt

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Message-ID: <20221130171715.nujptzwnut7silbm@pengutronix.de>
Date:   Wed, 30 Nov 2022 18:17:15 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Markus Schneider-Pargmann <msp@...libre.com>
Cc:     Chandrasekar Ramakrishnan <rcsekar@...sung.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/15] can: m_can: Use transmit event FIFO watermark
 level interrupt

On 16.11.2022 21:52:57, Markus Schneider-Pargmann wrote:
> Currently the only mode of operation is an interrupt for every transmit
> event. This is inefficient for peripheral chips. Use the transmit FIFO
> event watermark interrupt instead if the FIFO size is more than 2. Use
> FIFOsize - 1 for the watermark so the interrupt is triggered early
> enough to not stop transmitting.
> 
> Note that if the number of transmits is less than the watermark level,
> the transmit events will not be processed until there is any other
> interrupt. This will only affect statistic counters. Also there is an
> interrupt every time the timestamp wraps around.
> 
> Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>

Please make this configurable with the ethtool TX IRQ coalescing
parameter. Please setup an hwtimer to enable the regular interrupt after
some configurable time to avoid starving of the TX complete events.

I've implemented this for the mcp251xfd driver, see:

656fc12ddaf8 ("can: mcp251xfd: add TX IRQ coalescing ethtool support")
169d00a25658 ("can: mcp251xfd: add TX IRQ coalescing support")
846990e0ed82 ("can: mcp251xfd: add RX IRQ coalescing ethtool support")
60a848c50d2d ("can: mcp251xfd: add RX IRQ coalescing support")
9263c2e92be9 ("can: mcp251xfd: ring: add support for runtime configurable RX/TX ring parameters")

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
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