From mboxrd@z Thu Jan  1 00:00:00 1970
From: Bryan O'Donoghue <pure.logic@nexus-software.ie>
Subject: Re: [PATCH 2/2 v2] SPI: spi-pxa2xx: SPI support for Intel Quark X1000
Date: Wed, 08 Oct 2014 10:02:07 +0100
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	<linux-arm-kernel@lists.infradead.org>,
	"linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Westerberg, Mika" <mika.westerberg@intel.com>,
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	"Ong, Boon Leong" <boon.leong.ong@intel.com>,
	"Tan, Raymond" <raymond.tan@intel.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: "Chen, Alvin" <alvin.chen@intel.com>,
	Eric Miao <eric.y.miao@gmail.com>,
	Russell King <linux@arm.linux.org.uk>,
	Haojian Zhuang <haojian.zhuang@gmail.com>,
	Mark Brown <broonie@kernel.org>
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On 08/10/14 08:48, Chen, Alvin wrote:

> Now, we have another board which can support 4 slave spi per master, but not only Galileo. Since that board is not public, after discussing with team, we decide to make the
> upstream code to support '1'.
>
> I will change it back to
> .num_chipselect = 1,

Hi Alvin.

The important thing in terms of Galileo is to ensure that a GPIO can be 
used for chip-select.

The user-space API ported from Arduino to Linux wants to control it's 
own chip-select directly - so the internal chip-select of the Quark SPI 
master can - and does de-assert while doing SPI transactions on Galileo. 
The CS on the master is tied to FIFO occupancy - so at higher bit-rates 
we can fail to keep the FIFO occupied :(

That doesn't matter though, because the pinned out SPI:CS on the Arduino 
header is a GPIO.

 From the perspective of the Arduino code in user-space and the slave 
hardware @ the other end of the SPI bus - we see a nice and consistent 
chip-select for the entire duration of the SPI transaction - even though 
the actual SPI:CS coming from the SoC can *waggle* - when FIFOs go empty.

IMO - so long as you've tested on Galileo and seen working SPI - you're 
good to go anyway.

Bryan