linux-kernel - Re: [PATCH 1/2] dt-bindings: mtd: spi-nor: Add output-driver-strength property

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Message-ID: <0cf4389f-cb91-44aa-a4be-48878d1221de@microchip.com>
Date:   Mon, 4 Oct 2021 11:25:29 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <Alexander.Stein@...systems.com>, <miquel.raynal@...tlin.com>,
        <richard@....at>, <vigneshr@...com>, <robh+dt@...nel.org>,
        <p.yadav@...com>, <michael@...le.cc>
CC:     <alexander.stein@...tq-group.com>, <linux-mtd@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings: mtd: spi-nor: Add output-driver-strength
 property

On 10/4/21 2:15 PM, Alexander Stein wrote:
> [You don't often get email from alexander.stein@...systems.com. Learn why this is important at http://aka.ms/LearnAboutSenderIdentification.]
> 
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> From: Alexander Stein <alexander.stein@...tq-group.com>
> 
> This property is for optimizing output voltage impedance and is
> specific to each board.
> 
> Signed-off-by: Alexander Stein <alexander.stein@...tq-group.com>
> ---
> I checked Micron and Macronix datasheets. Both have similar but not
> identical supported values. Also the register locations are different.
> For those reasons I decided to specify the Ohms value directly and let
> the device specfic driver figure out if it is supported where to write
> it to.
> BTW: Are the Ohm values and the corresponding register bits standardized
> somewhere?

Please check JEDEC Standard No. 216D.01, I see a SCCR Map which defines Output
Driver Strength values.

> 
>  Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> index ed590d7c6e37..7d7f20a741b5 100644
> --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> @@ -72,6 +72,12 @@ properties:
>        be used on such systems, to denote the absence of a reliable reset
>        mechanism.
> 
> +  output-driver-strength:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      Output driver strength in Ohms which optimizes the impedance at Vcc/2
> +      output voltage.
> +
>    label: true
> 
>    partitions:
> --
> 2.25.1
>