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 16:37:09 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Michael Walle <michael@...le.cc>
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

On 12/03/21 11:20AM, Michael Walle wrote:
> 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.

The algorithm supports a temperature range of -45 C to +130 C. The 
temperature is checked at calibration time and adjustments are made to 
make sure the reads work over the entire temperature range [0].

[0] The current implementation does not have a way to query the 
temperature from the sensor (see cqspi_get_temp()), so it always assumes 
the temperature at calibration time is 45 C. But that can be added later 
once the temperature sensor driver is implemented.

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.