linux-kernel - Re: [PATCH v2 2/3] fpga manager: framework core

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Date:	Fri, 24 Oct 2014 09:54:00 -0500
From:	atull <atull@...nsource.altera.com>
To:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
CC:	Pavel Machek <pavel@...x.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<jgunthorpe@...idianresearch.com>, <hpa@...or.com>,
	Michal Simek <monstr@...str.eu>, <michal.simek@...inx.com>,
	<rdunlap@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <robh+dt@...nel.org>,
	Grant Likely <grant.likely@...aro.org>, <iws@...o.caltech.edu>,
	<linux-doc@...r.kernel.org>, Mark Brown <broonie@...nel.org>,
	<philip@...ister.org>, <rubini@...dd.com>,
	Steffen Trumtrar <s.trumtrar@...gutronix.de>,
	<jason@...edaemon.net>, <kyle.teske@...com>, <nico@...aro.org>,
	Felipe Balbi <balbi@...com>, <m.chehab@...sung.com>,
	<davidb@...eaurora.org>, Rob Landley <rob@...dley.net>,
	<davem@...emloft.net>, <cesarb@...arb.net>,
	<sameo@...ux.intel.com>, <akpm@...ux-foundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alan Tull <delicious.quinoa@...il.com>,
	<dinguyen@...nsource.altera.com>, <yvanderv@...nsource.altera.com>
Subject: Re: [PATCH v2 2/3] fpga manager: framework core

On Fri, 24 Oct 2014, Pantelis Antoniou wrote:

> Hi Pavel,
> 
> > On Oct 24, 2014, at 1:52 PM, Pavel Machek <pavel@...x.de> wrote:
> > 
> > Hi!
> > 
> >> * /sys/class/fpga_manager/<fpga>/firmware
> >>  Name of FPGA image file to load using firmware class.
> >>  $ echo image.rbf > /sys/class/fpga_manager/<fpga>/firmware
> > 
> > I .. still don't think this is good idea. What about namespaces?
> > The path corresponds to path in which namespace?
> > 

Hi Pavel,

Sorry if my documentation is too brief here.  The context is the
firmware class.  The 'image.rbf' is a image file that is located
on the filesystem in the firmware search patch.
See Documentation/firmware_class/README.

Basically we need some way of loading a FPGA image to the FPGA.
I don't think any one way is going to meet everybody's needs so
I wanted to export enough functions from fpga-mgr.c that other
interfaces can by built.  I think firmware will work just fine
for some people and it is great in that it already exists in the
kernel.

If I missed your point, please let me know.

> 
> FWIW the overlays patchset uses binary configfs attribute to make this work.
> 

Hi Pantelis,

Yes I think you've mentioned that before.  So that would be another
way of giving a device tree overlay to configfs, right?  I should
that to the documentation in the patch header.

> >> +int fpga_mgr_write(struct fpga_manager *mgr, const char *buf, size_t count)
> >> +{
> >> +	int ret;
> >> +
> >> +	if (test_and_set_bit_lock(FPGA_MGR_BUSY, &mgr->flags))
> >> +		return -EBUSY;
> >> +
> >> +	dev_info(mgr->dev, "writing buffer to %s\n", mgr->name);
> >> +
> >> +	ret = __fpga_mgr_write(mgr, buf, count);
> >> +	clear_bit_unlock(FPGA_MGR_BUSY, &mgr->flags);
> >> +
> >> +	return ret;
> >> +}
> >> +EXPORT_SYMBOL_GPL(fpga_mgr_write);
> > 
> > Is the EBUSY -- userspace please try again, but you don't know when to
> > try again -- right interface? I mean, normally kernel would wait, so
> > that userland does not have to poll?
> > 

Yes, for fpga_mgr_write it may be more useful for this to be
a blocking call.

> >> +static ssize_t fpga_mgr_firmware_store(struct device *dev,
> >> +				       struct device_attribute *attr,
> >> +				       const char *buf, size_t count)
> >> +{
> >> +	struct fpga_manager *mgr = dev_get_drvdata(dev);
> >> +	unsigned int len;
> >> +	char image_name[NAME_MAX];
> >> +	int ret;
> >> +
> >> +	/* lose terminating \n */
> >> +	strcpy(image_name, buf);
> >> +	len = strlen(image_name);
> >> +	if (image_name[len - 1] == '\n')
> >> +		image_name[len - 1] = 0;
> >> +
> >> +	ret = fpga_mgr_firmware_write(mgr, image_name);
> >> +	if (ret)
> >> +		return ret;
> >> +
> >> +	return count;
> >> +}
> > 
> > This shows why the interface is not right... Valid filename may
> > contain \n, right? It may even end with \n.
> > 
> 
> I could argue that a valid firmware file is one that’s well formed and does not
> contain those characters.
> 
> I guess this is only for make echo file >foo work. You could specify that echo -n file >foo is
> required.
> 

I am accustomed to doing 'echo -n' for most of sysfs anyway.  Once in a
while I am a bonehead and forget the '-n' and spend a few minutes
wondering why this thing that worked last week suddenly rejects all
commands.  I'm just trying to make my user interface a bit user-friendly.

I will take out the '\n' stripping and update the documentation.  I didn't
realize this would be controversial.

Alan

> 
> > Best regards,
> > 									Pavel
> > -- 
> > (english) http://www.livejournal.com/~pavelmachek
> > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
> 
> Regards
> 
> — Pantelis
> 
>