Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII;
 format=flowed
Content-Transfer-Encoding: 7bit
Date:   Fri, 12 Mar 2021 14:32:25 +0100
From:   Michael Walle <michael@walle.cc>
To:     Pratyush Yadav <p.yadav@ti.com>
Cc:     Nishanth Menon <nm@ti.com>, Tero Kristo <kristo@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Tudor Ambarus <tudor.ambarus@microchip.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Mark Brown <broonie@kernel.org>,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
        linux-spi@vger.kernel.org, Lokesh Vutla <lokeshvutla@ti.com>
Subject: Re: [RFC PATCH 0/6] spi: Add OSPI PHY calibration support for
 spi-cadence-quadspi
In-Reply-To: <20210311191216.7363-1-p.yadav@ti.com>
References: <20210311191216.7363-1-p.yadav@ti.com>
User-Agent: Roundcube Webmail/1.4.11
Message-ID: <b9450a151cce89cde47b4d6a76c74b32@walle.cc>
Precedence: bulk

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