linux-kernel - RE: [RFC PATCH 0/2] spi: add dual parallel & stacked mode support in Zynq MPSoC GQSPI controller

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Date:	Wed, 15 Jul 2015 14:12:54 +0000
From:	Ranjit Abhimanyu Waghmode <ranjit.waghmode@...inx.com>
To:	Mark Brown <broonie@...nel.org>
CC:	Michal Simek <michals@...inx.com>,
	Soren Brinkmann <sorenb@...inx.com>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"computersforpeace@...il.com" <computersforpeace@...il.com>,
	"zajec5@...il.com" <zajec5@...il.com>,
	"marex@...x.de" <marex@...x.de>,
	"shijie.huang@...el.com" <shijie.huang@...el.com>,
	"juhosg@...nwrt.org" <juhosg@...nwrt.org>,
	"ben@...adent.org.uk" <ben@...adent.org.uk>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Harini Katakam <harinik@...inx.com>,
	"Punnaiah Choudary Kalluri" <punnaia@...inx.com>,
	"ran27jit@...il.com" <ran27jit@...il.com>
Subject: RE: [RFC PATCH 0/2] spi: add dual parallel & stacked mode support
 in Zynq MPSoC GQSPI controller

Hi Mark,

> > What is dual parallel mode?
> > ---------------------------
> > ZynqMP GQSPI controller supports Dual Parallel mode with following
> functionalities:
> > 1) Supporting two SPI flash memories operating in parallel. 8 I/O lines.
> > 2) Chip selects and clock are shared to both the flash devices
> > 3) This mode is targeted for faster read/write speed and also doubles the size
> > 4) Commands/data can be transmitted/received from both the devices(mirror),
> >    or only upper or only lower flash memory devices.
> > 5) Data arrangement:
> >    With stripe enabled,
> >    Even bytes i.e. 0, 2, 4,... are transmitted on Lower Data Bus
> >    Odd bytes i.e. 1, 3, 5,.. are transmitted on Upper Data Bus.
> 
> For the SPI code this just seems like SPI with an 8 bit data width.
> 
> > What is stacked mode?
> > ---------------------
> > ZynqMP GQSPI controller supports stacked mode with following
> functionalities:
> > 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 performance
> >    improvement when compared with single.
> 
> This is just a normal SPI controller from a SPI point of view.

How can we really represent the stacked mode in current configuration?

Thanks & Regards,
Ranjit
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