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

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Date:	Thu, 6 Aug 2015 12:23:53 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	"R, Vignesh" <vigneshr@...com>,
	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 Thu, Aug 06, 2015 at 12:01:37PM +0200, Michal Suchanek wrote:

> 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.

But what in concrete terms is that supposed to mean?  It's currently
just an essentially undocumented flag on a message rather than something
operating at the level of a flash chip.  That's pretty much where
Russell's comments come from.

> If I was using m25p80.c to talk to anything but an actual flash chip
> it would get me quite worried.

Sure, but at the end of the day it's just emitting standard SPI messages
which don't know anything about flash.  If those messages are a sensible
interface here then why bother with the flag, we can just pattern match
on the format of the message.  If that doesn't work then probably this
isn't a great interface and a separate, application specific interface
makes more sense.

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