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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 10C7CC433FE for ; Wed, 22 Dec 2021 08:23:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232950AbhLVIX3 convert rfc822-to-8bit (ORCPT ); Wed, 22 Dec 2021 03:23:29 -0500 Received: from relay9-d.mail.gandi.net ([217.70.183.199]:58557 "EHLO relay9-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230306AbhLVIX3 (ORCPT ); Wed, 22 Dec 2021 03:23:29 -0500 Received: (Authenticated sender: miquel.raynal@bootlin.com) by relay9-d.mail.gandi.net (Postfix) with ESMTPSA id 073C6FF807; Wed, 22 Dec 2021 08:23:25 +0000 (UTC) Date: Wed, 22 Dec 2021 09:23:24 +0100 From: Miquel Raynal To: Pratyush Yadav Cc: Rob Herring , , Michal Simek , Thomas Petazzoni , Mark Brown , , Richard Weinberger , Vignesh Raghavendra , Tudor Ambarus , Michael Walle , , Rob Herring Subject: Re: [PATCH v5 1/3] dt-bindings: mtd: spi-nor: Allow two CS per device Message-ID: <20211222092324.7ec6ec6a@xps13> In-Reply-To: <20211221184725.46lelrdfoxeom6uc@ti.com> References: <20211221170058.18333-1-miquel.raynal@bootlin.com> <20211221170058.18333-2-miquel.raynal@bootlin.com> <20211221184725.46lelrdfoxeom6uc@ti.com> Organization: Bootlin X-Mailer: Claws Mail 3.17.7 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-spi@vger.kernel.org Hi Pratyush, p.yadav@ti.com wrote on Wed, 22 Dec 2021 00:17:27 +0530: > On 21/12/21 06:00PM, Miquel Raynal wrote: > > The Xilinx QSPI controller has two advanced modes which allow the > > controller to behave differently and consider two flashes as one single > > storage. > > > > One of these two modes is quite complex to support from a binding point > > of view and is the dual parallel memories. In this mode, each byte of > > data is stored in both devices: the even bits in one, the odd bits in > > the other. The split is automatically handled by the QSPI controller and > > is transparent for the user. > > > > The other mode is simpler to support, it is called dual stacked > > memories. The controller shares the same SPI bus but each of the devices > > contain half of the data. Once in this mode, the controller does not > > follow CS requests but instead internally wires the two CS levels with > > the value of the most significant address bit. > > > > Supporting these two modes will involve core changes which include the > > possibility of providing two CS for a single SPI device > > > > Signed-off-by: Miquel Raynal > > Acked-by: Rob Herring > > --- > > Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml > > index 39421f7233e4..4abfb4cfc157 100644 > > --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml > > +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml > > @@ -47,7 +47,8 @@ properties: > > identified by the JEDEC READ ID opcode (0x9F). > > > > reg: > > - maxItems: 1 > > + minItems: 1 > > + maxItems: 2 > > You allow up to 4 items in stacked-memories but only allow up to 2 CS, > which would make the other 2 memories unusable. Should also change this > to 4. Yes, I allowed "more" theoretical devices in the stacked/parallel-memories properties because there is no real limitation on this side so I didn't want to constrain it too much, while still keeping a maximum value, hence 4 seemed a nice guess for a "maximum but can be bigger value we don't really care it's just for bounding". However on the SPI side this is a big change with deep consequences and I don't want to rush things so it is on purpose that I kept the limitation to 2. But we can change the maxItems to 2 everywhere if this appears to be the thing to do. Thanks, Miquèl