linux-kernel - Re: [PATCH v2 1/2] gpio: Add driver for Zynq GPIO controller

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Message-ID: <20140711122744.GE3003@tarshish>
Date:	Fri, 11 Jul 2014 15:27:44 +0300
From:	Baruch Siach <baruch@...s.co.il>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Sören Brinkmann <soren.brinkmann@...inx.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexandre Courbot <gnurou@...il.com>,
	Harini Katakam <harinik@...inx.com>,
	Pawel Moll <pawel.moll@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Michal Simek <michal.simek@...inx.com>,
	Harini Katakam <harinikatakamlinux@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Rob Landley <rob@...dley.net>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	Harini Katakam <harini.katakam@...inx.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/2] gpio: Add driver for Zynq GPIO controller

Hi Linus,

On Fri, Jul 11, 2014 at 02:06:29PM +0200, Linus Walleij wrote:
> On Fri, Jul 11, 2014 at 8:28 AM, Baruch Siach <baruch@...s.co.il> wrote:
> > On Tue, Jul 08, 2014 at 11:27:57AM +0200, Linus Walleij wrote:
> 
> >> What is the usecase here?
> >
> > During boot I need to know, for example, when an FPGA is ready to be
> > programmed, and when said FPGA has finished its initialization. I also read
> > the sate of on-board DIP switches to determine the desired boot method. I find
> > the current sysfs interface quite convenient for these and similar tasks.
> 
> So given that an FPGA is a piece of hardware, it should have its firmware
> loaded from the kernel and a kernel driver communicating with it I guess?
> 
> I feel the smell of a huge bundle of userspace drivers for something that
> should be handled by the kernel.

The FPGA can be loaded using simple SPI bit-banging, for which I used the 
userspace SPI interface. Nothing fancy, just a few hundred LoC. Kernel driver 
along with a userspace interface to be maintained forever for this task seems 
an overkill to me.

baruch

-- 
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