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Message-ID: <559F824B.70409@topic.nl>
Date: Fri, 10 Jul 2015 10:28:59 +0200
From: Mike Looijmans <mike.looijmans@topic.nl>
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To: Ranjit Waghmode <ranjit.waghmode@xilinx.com>, <broonie@kernel.org>,
 <michal.simek@xilinx.com>, <soren.brinkmann@xilinx.com>,
 <dwmw2@infradead.org>, <computersforpeace@gmail.com>, <zajec5@gmail.com>,
 <marex@denx.de>, <shijie.huang@intel.com>, <juhosg@openwrt.org>,
 <ben@decadent.org.uk>
CC: <harinik@xilinx.com>, <linux-kernel@vger.kernel.org>,
 <linux-spi@vger.kernel.org>, <linux-mtd@lists.infradead.org>,
 <punnaia@xilinx.com>, <ran27jit@gmail.com>,
 <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH 0/2] spi: add dual parallel & stacked mode support
 in Zynq MPSoC GQSPI controller
References: <1436445895-25504-1-git-send-email-ranjit.waghmode@xilinx.com>
In-Reply-To: <1436445895-25504-1-git-send-email-ranjit.waghmode@xilinx.com>
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=EF=BB=BFOn 09-07-15 14:44, Ranjit Waghmode wrote:
> This series of patches is to add dual parallel and stacked mode support f=
or
> Zynq Ultrascale+ MPSoC GQSPI controller driver.
>
> These are all very high level changes and expected to make an idea clear.
> Comments and suggestions are welcomed.
>
...
>
> What is stacked mode?
> ---------------------
> ZynqMP GQSPI controller supports stacked mode with following functionalit=
ies:
> 1) The Generic Quad-SPI controller also supports two SPI flash memories
>     in a shared bus arrangement to reduce IO pin count.
> 2) Separate chip select lines
> 3) Shared I/O lines
> 4) This mode is targeted for increasing the flash memory and no performan=
ce
>     improvement when compared with single.

One could also model the stacked mode as having two distinct flash chips wi=
th=20
separate chip selects and shared lines.
Merging them into a single storage device can be done on block layer or hig=
her=20
level. This allows the flash chips to be used in any configuration using=20
existing support for concatenating multiple devices.
I think this would be a more generic way of doing this. It also allows much=
=20
more flexibility, for example the devices could be used in a mirror setup, =
or=20
in combination with additional devices on other controllers.


Kind regards,

Mike Looijmans
System Expert

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