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

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Message-ID: <CAD6G_RQhWBsUTZNBB44W98Fjzw82H_D_E9nY0aDWezj729mkoA@mail.gmail.com>
Date:	Wed, 26 Aug 2015 17:49:59 +0530
From:	Jagan Teki <jteki@...nedev.com>
To:	Ranjit Waghmode <ranjit.waghmode@...inx.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>, broonie@...nel.org,
	Michal Simek <michal.simek@...inx.com>,
	Soren Brinkmann <soren.brinkmann@...inx.com>, zajec5@...il.com,
	ben@...adent.org.uk, Marek Vašut <marex@...x.de>,
	Huang Shijie <b32955@...escale.com>, knut.wohlrab@...bosch.com,
	juhosg@...nwrt.org, beanhuo@...ron.com,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-spi@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, harinik@...inx.com,
	punnaia@...inx.com
Subject: Re: [LINUX RFC v2 0/4] spi: add dual parallel mode support in Zynq
 MPSoC GQSPI controller

On 26 August 2015 at 11:56, Ranjit Waghmode <ranjit.waghmode@...inx.com> 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 series also updated MTD layer files for adding parallel mode support.
>
> 1) Added Support for two flashes
> 2) Support to enable/disable data stripe as and when required.
> 3) Added required parameters to spi_nor structure. Initialized all
>    added parameters in spi_nor_scan()
> 4) Added support for dual parallel in spi_nor_read/write/erase functions by:
>    a) Increasing page_size, sector_size, erase_size and toatal flash size
>       as and when required.
>    b) Dividing address by 2
>    c) Updating spi->master->flags for qspi driver to change CS
> 5) Updated read_sr() to get status of both flashes
> 6) Also updated read_fsr() to get status of both flashes
>
> These all are very high level changes and expected to make an idea clear.
> Comments and suggestions are always welcomed
>
> ---
> V2 Changes:
> a) Splitted patches based on logical changes
> b) Added error handling for newly added APIs in SPI core
> ---
>
> Ranjit Waghmode (4):
>   spi: add support of two chip selects & data stripe
>   mtd: add spi_device instance to spi_nor struct
>   spi-nor: add dual parallel mode support
>   spi: zynqmp: gqspi: add support for dual parallel mode configuration

I don't find any previous discussion about way to inform flash
dual-ness into spi-nor
from spi drivers.

Here is my idea, probably others may think same.
Informing dual_flash from drivers/spi through flags or any other mode
bits is not a better approach as dual flash feature is specific to
spi-nor flash controller (controller specially designed for spi-nor
flash not the generic spi controller).  So if the driver sits on
drivers/mtd/spi-nor/ (ex: fsl-quadspi.c), may be we can inform flash
specific things to spi-nor as it's not touching generic spi stack in
Linux. But there is a defined-drawback if the driver is moved to
drivers/mtd/spi-nor ie it can't use spi core API's at-all.

thanks!
-- 
Jagan | openedev.
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