From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BE021C433EF for ; Tue, 12 Oct 2021 07:49:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9F8D860D42 for ; Tue, 12 Oct 2021 07:49:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234411AbhJLHvJ (ORCPT ); Tue, 12 Oct 2021 03:51:09 -0400 Received: from ssl.serverraum.org ([176.9.125.105]:52747 "EHLO ssl.serverraum.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232541AbhJLHu4 (ORCPT ); Tue, 12 Oct 2021 03:50:56 -0400 Received: from ssl.serverraum.org (web.serverraum.org [172.16.0.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ssl.serverraum.org (Postfix) with ESMTPSA id DD8A822205; Tue, 12 Oct 2021 09:48:46 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=walle.cc; s=mail2016061301; t=1634024927; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XTY/Z+zotHcX5KpcuZaorS0sZpvLJgkD21qg7w9gSRQ=; b=LWsI1mI6pSamxpDS/0+dFr2odTpKKzNiH6/1yG4SErONEZ2/U+oBsSryCX6kdka0owzZMP DhXdqjh+2CuV/P8auid/ozf8cdDxmpTGrRZc1+gBbUPCEgCMQeKqfe6uxsO40QV3wn5VNG E5LGJih/KiyGiPJztKa8y0OH1XN3seM= MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 12 Oct 2021 09:48:46 +0200 From: Michael Walle To: Alexander Stein Cc: Miquel Raynal , Richard Weinberger , Vignesh Raghavendra , Rob Herring , Pratyush Yadav , Tudor Ambarus , linux-mtd@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] dt-bindings: mtd: spi-nor: Add output-driver-strength property In-Reply-To: <20211012061704.284214-1-alexander.stein@ew.tq-group.com> References: <20211012061704.284214-1-alexander.stein@ew.tq-group.com> User-Agent: Roundcube Webmail/1.4.11 Message-ID: X-Sender: michael@walle.cc Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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