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 22:30:02 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Michael Walle <michael@...le.cc>
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

On 12/03/21 02:32PM, Michael Walle wrote:
> 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.

I haven't seen any such flash but it looks like Tudor has.

> 
> -michael

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.