Re: [LINUX RFC v2 0/4] spi: add dual parallel mode support in Zynq MPSoC GQSPI controller

[Marek Vasut]

On Wednesday, September 02, 2015 at 07:12:14 PM, Ranjit Abhimanyu Waghmode 
wrote:
> Hi Marek,
> 
> > -----Original Message-----
> > From: Marek Vasut [mailto:marex@xxxxxxx]
> > Sent: Wednesday, August 26, 2015 12:26 PM
> > To: Ranjit Abhimanyu Waghmode
> > Cc: dwmw2@xxxxxxxxxxxxx; computersforpeace@xxxxxxxxx;
> > broonie@xxxxxxxxxx; Michal Simek; Soren Brinkmann; zajec5@xxxxxxxxx;
> > ben@xxxxxxxxxxxxxxx; b32955@xxxxxxxxxxxxx; knut.wohlrab@xxxxxxxxxxxx;
> > juhosg@xxxxxxxxxxx; beanhuo@xxxxxxxxxx; linux-mtd@xxxxxxxxxxxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx; linux-spi@xxxxxxxxxxxxxxx; linux-arm-
> > kernel@xxxxxxxxxxxxxxxxxxx; Harini Katakam; Punnaiah Choudary Kalluri
> > Subject: Re: [LINUX RFC v2 0/4] spi: add dual parallel mode support in
> > Zynq MPSoC GQSPI controller
> > 
> > On Wednesday, August 26, 2015 at 08:26:03 AM, Ranjit Waghmode wrote:
> > > This series adds dual parallel mode support for Zynq Ultrascale+ MPSoC
> > > GQSPI controller driver.
> > > 
> > > 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.
> > 
> > This might be a dumb question, but why don't you just treat this as an
> > SPI NOR flash with 8-bit bus ?
> 
> In case of dual parallel configuration of this controller there are
> different modes like single, dual and quad mode. Whatever you are
> suggesting would fit only in the case of Quad mode operation as both buses
> would have 4 lines each. In case of single mode of parallel configuration,
> there would be two buses; but the line on each bus would one. So
> altogether there will be two lines. And in case of dual mode of parallel
> configuration each bus will be having two lines. So altogether 4 lines
> will be there. So keeping 8 lines would not support above two modes of
> parallel configuration correctly.
> 
> Logically it is a single flash with 8 IO lines but physically it's a two
> flash devices and each has 4 IO lines. So, in this case, read and write
> addresses should be always even and minimum data that can be accessed is 2
> bytes.

Oh, I see what the issue is now. It has to do with configuring the flash
into correct bus-width mode, right ?

Best regards,
Marek Vasut
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