linux-kernel - Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read

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Date:	Thu, 6 Aug 2015 13:02:29 +0200
From:	Michal Suchanek <hramrach@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Mark Brown <broonie@...nel.org>, "R, Vignesh" <vigneshr@...com>,
	devicetree <devicetree@...r.kernel.org>,
	Brian Norris <computersforpeace@...il.com>,
	Tony Lindgren <tony@...mide.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-spi <linux-spi@...r.kernel.org>,
	Huang Shijie <b32955@...escale.com>,
	MTD Maling List <linux-mtd@...ts.infradead.org>,
	linux-omap@...r.kernel.org, David Woodhouse <dwmw2@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read

On 6 August 2015 at 12:22, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Thu, Aug 06, 2015 at 12:01:37PM +0200, Michal Suchanek wrote:
>> Disclaimer: I am not familiar with the hardware for which this patch
>> adds support.
>>
>> However, I am familiar m25p80.c and as I understand it the controller
>> is basically supposed to implement m25p80.c in hardware when this flag
>> is set.
>
> That, to me, sounds like what you have is:
>
> ---m25p80 specific interface--->SPI bus--->m25p80 device
>
> Where the m25p80 specific interface does not expose direct access to the
> SPI bus?

The m25p80 specific hardware interface is presumably optional so you
can use it or not. The description is a bit vague, though.

In fsl-qspi the driver does not make it optional. I am not sure that
controller can be used for non-m25p80 slaves.


>
> If that's the case, then maybe you should consider whether using the SPI
> bus infrastructure is really the best way forward.  Would it make more
> sense instead to adopt a different software structure, something more
> high-level like:
>
>      +-------------------------------------------+
>      |          m25p80 high-level driver      =spi-nor   |
>      +----------------------+--------------------+
>      |   SPI m25p80 driver  |                    |
>      +----------------------+                    |
>      |      SPI layer       |  Special driver    =fsl-qspi|
>      +----------------------+                    |
>      |    SPI bus driver    |                    |
>      +----------------------+--------------------+
>      |     SPI hardware     |  Special hardware  |
>      +----------------------+--------------------+
>

Thanks

Michal
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