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;
Date:   Fri, 12 Mar 2021 16:37:09 +0530
From:   Pratyush Yadav <p.yadav@ti.com>
To:     Michael Walle <michael@walle.cc>
CC:     <Tudor.Ambarus@microchip.com>, <nm@ti.com>, <kristo@kernel.org>,
        <robh+dt@kernel.org>, <miquel.raynal@bootlin.com>,
        <richard@nod.at>, <vigneshr@ti.com>, <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>,
        <lokeshvutla@ti.com>
Subject: Re: [RFC PATCH 0/6] spi: Add OSPI PHY calibration support for
 spi-cadence-quadspi
Message-ID: <20210312110707.lrabch4ketqyyepn@ti.com>
References: <20210311191216.7363-1-p.yadav@ti.com>
 <9c551f56-4c00-b41a-f051-8b7e197fbcdc@microchip.com>
 <20210312101036.jfz2733ssv4nhfey@ti.com>
 <676386736df5e5b22e34b0b5af91c894@walle.cc>
MIME-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <676386736df5e5b22e34b0b5af91c894@walle.cc>
User-Agent: NeoMutt/20171215
Precedence: bulk

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.