linux-kernel - Re: [PATCH 11/16] spi: bcm63xx-hsspi: Add prepend feature support

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Message-ID: <Y7iaEOBP4TRBoDYy@sirena.org.uk>
Date:   Fri, 6 Jan 2023 22:00:48 +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 11/16] spi: bcm63xx-hsspi: Add prepend feature support

On Fri, Jan 06, 2023 at 12:08:03PM -0800, William Zhang wrote:
> Multiple transfers within a SPI message may be combined into one
> transfer to the controller using its prepend feature. A SPI message is
> prependable only if the following are all true:
>   * One or more half duplex write transfer
>   * Optional full duplex read/write at the end
>   * No delay and cs_change between transfers

There is nothing driver specific here, this should be implemented in the
core - we have existing logic to rewrite messages to match driver
constraints, this could be added there possibly with flags to allow
drivers to disable or enable the merging if they've got special
requirements.

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