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

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Message-ID: <20230322155829.uecwlv23r7plgok4@skbuf>
Date:   Wed, 22 Mar 2023 17:58:29 +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 08:45:32AM -0700, Colin Foster wrote:
> The chip itself doesn't support bulk reads. Every register read must be
> "Chip Select \" > "Read+Address Command" > "Padding" > "One Register Value" >
> "Chip Select /"
> 
> Figure 74 of [1] shows "SI Read Timing in Fast Mode", but that is when
> the VSC751X is the SPI controller, not a SPI endpoint. i.e. when the
> VSC751X is reading _from_ an external flash chip. It also has a blurb
> about "After reading address n, the SI boot controller automatically
> continues reading address n+1".
> 
> Figure 63 shows "Read Sequence for One-Byte Padding" which is actually
> done when an external CPU is reading _from_ the VSC751X devices. There
> is no suggestion that address n+1 will be returned in this scenario.
> 
> [1] https://ww1.microchip.com/downloads/en/DeviceDoc/VMDS-10489.pdf
> 
> I can update the commit message as needed.

I have no further comment. From my perspective, resending the patch is
not needed.