linux-kernel - Re: [Patch V2] spi/tegra114: Correct support for cs

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Date:	Fri, 27 Sep 2013 14:25:11 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Rhyland Klein <rklein@...dia.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Laxman Dewangan <ldewangan@...dia.com>,
	Thierry Reding <thierry.reding@...il.com>,
	linux-spi@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org, Simon Glass <sjg@...omium.org>,
	Olof Johansson <olof@...om.net>
Subject: Re: [Patch V2] spi/tegra114: Correct support for cs_change

On Thu, Sep 26, 2013 at 01:01:43PM -0400, Rhyland Klein wrote:
> The tegra114 driver wasn't currently handling the cs_change
> functionality. cs_change is meant to invert the decisions of whether
> or not to deactivate CS after each transfer. Without cs_change, after
> every transfer (other than the last in the message) the normal behavior
> is to leave CS active. For the last transfer, normally CS is
> deactivated when the transfer is complete.

Applied, thanks.

One thing I've got planned is to build on the existing factoring out of
the queue code so that we have several operations decomposing the
message transfer, something like:

 - Set /CS
 - Map/unmap data to be transferred
 - Actually transfer data

partly to avoid issues such as the one you're seeing here with fiddly
stuff like /CS and partly because the mapping operations should be the
same for many devices, as should the /CS manipulation for devices using
GPIOs.

I've started working on this today.

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