linux-kernel - Re: [PATCH 14/16] spi: bcm63xx-hsspi: prepend: Disable spi mem dual io read op support

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Date:   Fri, 6 Jan 2023 22:07:32 +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 14/16] spi: bcm63xx-hsspi: prepend: Disable spi mem dual
 io read op support

On Fri, Jan 06, 2023 at 12:08:06PM -0800, William Zhang wrote:
> In general the controller supports SPI dual mode operation but the
> particular SPI flash dual io read op switches from single mode in cmd
> phase to dual mode in address and data phase. This is not compatible
> with prepend operation where cmd and address are sent out through the
> prepend buffer and they must use same the number of io pins.
> 
> This patch disables these SPI flash dual io read ops through the mem_ops
> supports_op interface when prepend mode is used. This makes sure the SPI
> flash driver selects the compatible read ops at run time.

This suggests that your prepend mode is attempting to combine
incompatible transfers doesn't it?  Presumably other devices could
generate similar access patterns...

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