linux-kernel - Re: [PATCH v2 1/2] dt-bindings: mtd: spi-nor: Add output-driver-strength property

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <a347541ba3f8c76912d4afdb6dc64d4d@walle.cc>
Date:   Tue, 12 Oct 2021 09:48:46 +0200
From:   Michael Walle <michael@...le.cc>
To:     Alexander Stein <alexander.stein@...tq-group.com>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Pratyush Yadav <p.yadav@...com>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: mtd: spi-nor: Add
 output-driver-strength property

Am 2021-10-12 08:17, schrieb Alexander Stein:
> This property is for optimizing output voltage impedance and is
> specific to each board. It overwrites the default set by the flash
> device. Various flash devices support different impedances.
> 
> Signed-off-by: Alexander Stein <alexander.stein@...tq-group.com>
> ---
> Changes in v2:
> * Updated the property description and the commit message accordingly
> 
>  Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> index ed590d7c6e37..4c3c506a8853 100644
> --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> @@ -72,6 +72,14 @@ 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. This property overwrites the default set by the 
> flash
> +      device. This is board specific and should be determined by the
> +      manufacturer. Various flash devices support different 
> impedances.

Mh, this seems to be very tailored to this flash chip. Eg. the "Vcc/2", 
is
this something specific to this flash or is this some kind of common 
usage?
For example, Winbond flashes specifies the output driver strength in 
percent.
Settings are 25%, 50%, 75%, 100% there.

I'd have to ask a hardware guy, if one could convert between these two
representations of the driver strength.

Rob, do you know how is this case ususally handled? Can there be 
different
properties, like:

output-driver-strength-ohms
output-driver-strength-percent

or similar.

-michael