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

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Message-ID: <CAOMqctS=E-MgPYC_eHSFM0FVtbKufs4LthpMGOeAGQ4k1MvT3Q@mail.gmail.com>
Date:	Wed, 5 Aug 2015 07:57:40 +0200
From:	Michal Suchanek <hramrach@...il.com>
To:	Vignesh R <vigneshr@...com>
Cc:	Mark Brown <broonie@...nel.org>,
	devicetree <devicetree@...r.kernel.org>,
	Brian Norris <computersforpeace@...il.com>,
	Russell King <linux@....linux.org.uk>,
	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 5 August 2015 at 07:35, Vignesh R <vigneshr@...com> wrote:
>
>
> On 08/05/2015 10:51 AM, Michal Suchanek wrote:
>> Hello,
>>
>> On 4 August 2015 at 19:59, R, Vignesh <vigneshr@...com> wrote:
>>>
>>>
>>> On 8/4/2015 9:21 PM, Mark Brown wrote:
>>>> On Mon, Aug 03, 2015 at 10:27:19AM +0530, Vignesh R wrote:
>>>>

>>>
>>> TI QSPI controller has two blocks:
>>> 1. SPI_CORE: This is generic(normal) spi mode. This can be used to
>>> communicate with any SPI devices (serial flashes as well as non-flash
>>> devices like touchscreen).
>>> 2. SFI_MM_IF(SPI memory mapped interface): The SFI_MM_IF block only
>>> allows reading and writing to an SPI flash device only. Used to speed up
>>> flash reads. It _cannot_ be used to communicate with non flash devices.
>>> Now, the spi_message that ti-qspi receives in transfer_one() callback
>>> can be from mtd device(in which case SFI_MM_IF can be used) or from any
>>> other non flash SPI device (in which case SFI_MM_IF must not be used
>>> instead SPI_CORE is to be used) but there is no way(is there?) to
>>> distinguish where spi_message is from. Therefore I introduced flag
>>> (use_mmap_mode) to struct spi_message. mtd driver will set flag to true,
>>> this helps the ti-qspi driver to determine that the user is flash device
>>> and thus can do read via SFI_MM_IF. If this flag is not set then the
>>> user is assumed to be non flash SPI driver and will use SPI_CORE block
>>> to communicate.
>>>
>>> On the whole, I just need a way to determine that the user is a flash
>>> device in order to switch to memory mapped interface.
>>>
>>
>> Maybe it can be set on the SPI slave rather than each message.
>
> You mean to add flag to spi_device struct? That's ok for me.
>

There are already mode flags so you can just add one more.

Thanks

Michal
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