linux-kernel - Re: [RFC PATCH 0/6] spi: Add OSPI PHY calibration support for spi-cadence-quadspi

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Date:   Fri, 12 Mar 2021 14:32:25 +0100
From:   Michael Walle <michael@...le.cc>
To:     Pratyush Yadav <p.yadav@...com>
Cc:     Nishanth Menon <nm@...com>, Tero Kristo <kristo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Mark Brown <broonie@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-spi@...r.kernel.org, Lokesh Vutla <lokeshvutla@...com>
Subject: Re: [RFC PATCH 0/6] spi: Add OSPI PHY calibration support for
 spi-cadence-quadspi

Am 2021-03-11 20:12, schrieb Pratyush Yadav:
> The main problem here is telling the controller where to find the
> pattern and how to read it. This RFC uses nvmem cells which point to a
> fixed partition containing the data to do the reads. It depends on [0]
> and [1].
> 
> The obvious problem with this is it won't work when the partitions are
> defined via command line. I don't see any good way to add nvmem cells 
> to
> command line partitions. I would like some help or ideas here. We don't
> necessarily have to use nvmem either. Any way that can cleanly and
> consistently let the controller find out where the pattern is stored is
> good.

The NXP LS1028A SoC has a similar calibration (although there its done
in hardware it seems) and there the datasheet mentions there are flash
devices which supports a preamble before a read function. The preamble
is then some kind of learning pattern. Did you see a flash which 
actually
supports that in the wild? I can't find any publicly available 
datasheets
of 8bit I/O SPI NOR flashes.

-michael