Re: SPI: DUAL/QUAD support

From: Sourav Poddar <sourav.poddar@ti.com>
To: yuhang wang <wangyuhang2014@gmail.com>,
	<Thomas.Betker@rohde-schwarz.com>
Cc: linux-mtd <linux-mtd-bounces@lists.infradead.org>,
	Johannes Stezenbach <js@sig21.net>,
	Grant Likely <grant.likely@secretlab.ca>,
	Mark Brown <broonie@kernel.org>,
	linux-mtd@lists.infradead.org,
	spi-devel-general@lists.sourceforge.net,
	linux-arm-kernel@lists.infradead.org
Subject: Re: SPI: DUAL/QUAD support
Date: Fri, 5 Jul 2013 13:10:01 +0530	[thread overview]
Message-ID: <51D67851.8020402@ti.com> (raw)
In-Reply-To: <CAHSAbzOg+uHndydSC43moF7pijc67pqzB2rPnY69ynXHEzw79g@mail.gmail.com>

On Friday 05 July 2013 11:55 AM, yuhang wang wrote:
> Hi Thomas:
>
>>> Well, there's two bits here.  One is the support in the client drivers
>>> for using the extra data lines and the other is the support in the SPI
>>> core for telling controllers to do this.  We need that second bit in
>>> place before the first one can be implemented.
>> I am not sure if we do. In the system I am working on, the QSPI controller
>> recognizes the quad mode commands from the Tx data and automatically
>> switches modes; no manual intervention by the flash driver is needed.
>>
>> I agree that this may not be the case for all SPI controllers. Yuhang, can
>> you tell us what your controller will do?
> OK, well my spi controller just sets the certain transfer mode in the register
> to make it in that mode(single,dual,quad). Then it will send and receive datas
> with the specific lines. As master, it should be told the transfer lines by the
> slave. Thus I need some members to deliver the information.
>

To add to all the discussion going on,
I am using a qspi controller with a spansion flash device.
I tried using quad read mode bit, and what is required to change in
my case is the following:

1. enable quad mode in flash configuration register.
2. change my read opcode to QUAD READ opcode according to flash datasheet.
3. Configure my qspi controller cmd reg to use 6 PIN whenever quad mode 
is used.

So,  I don't need to change things in spi framework to get
quad working. Though, as thomas also pointed out, it might
vary from controller to controller.

> But what you said "QSPI controller recognizes the quad mode commands
> from the Tx data and automatically switches modes;"  I can not figure out.
> The communication is launched by SPI master, so how can the controller
> recognizes the Tx data in the first transmission.
>
>> Yes, there are usually different opcodes, and as far as I know, they are
>> not supported by the m25p80 driver. It seems we are missing some
>> background info here.
>> My guess is that the flash chip in question is configured to treat single
>> mode opcodes as dual or quad mode commands (some chips support this), and
>> that the SPI controller needs to be told, for each transfer, which mode to
>> use.
> Just as Johannes said. In my patch m25p80's changes is incomplete.
> Because my inicial aim is to add the transfer width member to tell controller
> the mode flash in. And I will attach new patch about m25p80 later.
> Also you are right. There are really series of flashes do not support dual/quad
> transfer. So I don't know whether there are any standard for serial-flash just
> like the CFI for parallel-flash. Personally, to make a general standard and
> a general code for serial-flash is necessary. So that we do not need to add
> special function in m25p80.c.
>
> Thanks,
> yuhang
>
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