linux-kernel - Re: [PATCH 07/16] spi: bcm63xx-hsspi: Add polling mode support

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Message-ID: <Y7iW38Fsj0nIewDm@sirena.org.uk>
Date:   Fri, 6 Jan 2023 21:47:11 +0000
From:   Mark Brown <broonie@...nel.org>
To:     William Zhang <william.zhang@...adcom.com>
Cc:     Linux SPI List <linux-spi@...r.kernel.org>,
        Broadcom Kernel List <bcm-kernel-feedback-list@...adcom.com>,
        anand.gore@...adcom.com, tomer.yacoby@...adcom.com,
        dan.beygelman@...adcom.com, joel.peshkin@...adcom.com,
        f.fainelli@...il.com, jonas.gorski@...il.com,
        kursad.oney@...adcom.com, dregan@...l.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/16] spi: bcm63xx-hsspi: Add polling mode support

On Fri, Jan 06, 2023 at 12:07:59PM -0800, William Zhang wrote:

> Polling mode provides better throughput in general by avoiding the
> interrupt overhead as the maximum data size one interrupt can handle is
> only 512 bytes.

> When interrupt is not defined in the HSSPI dts node, driver switches to
> polling mode for controller SPI message processing.  Also add driver
> banner message when the driver is loaded successfully.

This should not be something the user selects via the DT, if the polling
mode is better then the driver should just use it regardless of there
being an interrupt wired up.  Generally there's some point at which the
benefits of polling become minimal (and the costs more impactful) but if
the DMA setup is as bad as it sounds then the driver should just ignore
the interrupt.

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