linux-kernel - Re: [PATCH v1 mfd] mfd: ocelot-spi: fix bulk read

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Date:   Wed, 22 Mar 2023 17:25:51 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Colin Foster <colin.foster@...advantage.com>
Cc:     linux-kernel@...r.kernel.org, Lee Jones <lee@...nel.org>
Subject: Re: [PATCH v1 mfd] mfd: ocelot-spi: fix bulk read

On Wed, Mar 22, 2023 at 07:11:30AM -0700, Colin Foster wrote:
> Ocelot chips (VSC7511, VSC7512, VSC7513, VSC7514) don't support bulk read
> operations over SPI.
> 
> Many SPI buses have hardware that can optimize consecutive reads.
> Essentially an address is written to the chip, and if the SPI controller
> continues to toggle the clock, subsequent register values are reported.
> This can lead to significant optimizations, because the time between
> "address is written to the chip" and "chip starts to report data" can often
> take a fixed amount of time.
> 
> When support for Ocelot chips were added in commit f3e893626abe ("mfd:
> ocelot: Add support for the vsc7512 chip via spi") it was believed that
> this optimization was supported. However it is not.

Details? What about bulk reads is "not supported", and not supported by whom?