linux-kernel - Re: [RFC PATCH 1/2] spi: Add support for Zynq QSPI controller

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Message-ID: <CAFcVECJvvch9Li0WihqoWcGNMMDVXfrujLUq6wvca46FztYpzA@mail.gmail.com>
Date:	Thu, 10 Jul 2014 18:09:55 +0530
From:	Harini Katakam <harinikatakamlinux@...il.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	linux-spi <linux-spi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Marek Vašut <marex@...x.de>,
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
	Geert Uytterhoeven <geert+renesas@...ux-m68k.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Jingoo Han <jg1.han@...sung.com>,
	Sourav Poddar <sourav.poddar@...com>,
	"michals@...inx.com" <michals@...inx.com>,
	Punnaiah Choudary Kalluri <punnaia@...inx.com>
Subject: Re: [RFC PATCH 1/2] spi: Add support for Zynq QSPI controller

Hi Mark,

On Thu, Jul 10, 2014 at 5:31 PM, Mark Brown <broonie@...nel.org> wrote:
> On Thu, Jul 10, 2014 at 04:03:19PM +0530, Harini Katakam wrote:
>
>> OK. Correct me if I'm wrong but announcing this support in master->flags is
>> just to say the controller supports it - Like Punnaiah mentioned in the other
>
> No, it's broken to set this if there is no ability to use it.
>
>> mail, nothing specific needs to be done from the controller driver to enable
>> dual/quad support. This is at the SOC/IP level.
>
> How does the client driver select the width to use for a transfer?

This controller is meant to be used only with flash devices.
The flash devices' supported width will be reflected in a table in MTD layer.
When selecting, priority is given to quad over dual and single in the MTD and
it will send commands using the supported tx/rx bus width accordingly.
About the supported bus width on board, tx-bus-width and rx-bus-width
properties in dts will have the info; which I believe spi core uses.

Regards,
Harini
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