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=UTF-8;
 format=flowed
Content-Transfer-Encoding: 8bit
Date:   Fri, 12 Mar 2021 14:26:50 +0100
From:   Michael Walle <michael@walle.cc>
To:     Pratyush Yadav <p.yadav@ti.com>
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
In-Reply-To: <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>
 <20210312110707.lrabch4ketqyyepn@ti.com>
User-Agent: Roundcube Webmail/1.4.11
Message-ID: <278f4417bad780ee610d86299e613990@walle.cc>
Precedence: bulk

Am 2021-03-12 12:07, schrieb Pratyush Yadav:
> 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].

Ah, nice. And you need the current temperature to correlate it to the
meassured timings, right?

-michael