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

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Message-ID: <676386736df5e5b22e34b0b5af91c894@walle.cc>
Date:   Fri, 12 Mar 2021 11:20:15 +0100
From:   Michael Walle <michael@...le.cc>
To:     Pratyush Yadav <p.yadav@...com>
Cc:     Tudor.Ambarus@...rochip.com, nm@...com, kristo@...nel.org,
        robh+dt@...nel.org, miquel.raynal@...tlin.com, richard@....at,
        vigneshr@...com, 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, lokeshvutla@...com
Subject: Re: [RFC PATCH 0/6] spi: Add OSPI PHY calibration support for
 spi-cadence-quadspi

Am 2021-03-12 11:10, schrieb Pratyush Yadav:
> There is usually a delay from when the flash drives the data line (IOW,
> puts a data bit on it) and when the signal reaches the controller. This
> delay can vary by the flash, board, silicon characteristics,
> temperature, etc.

Temperature might change over time, but the calibration is only done
once. I don't know how much influence the temperature actually has, but
our boards are usually operating from -40°C to +85°C. So there might be
a possible temperature difference of 125K between actual calibration and
when the flash is accessed.

-michael