linux-kernel - Re: [RFC PATCH] fpga: Introduce new fpga subsystem

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Date:	Mon, 23 Sep 2013 11:10:29 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Michal Simek <monstr@...str.eu>
Cc:	Yves Vandervennet <rocket.yvanderv@...il.com>,
	Alan Tull <atull@...era.com>,
	Jason Cooper <jason@...edaemon.net>,
	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dinh Nguyen <dinguyen@...era.com>,
	Philip Balister <philip@...ister.org>,
	Alessandro Rubini <rubini@...dd.com>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cesar Eduardo Barros <cesarb@...arb.net>,
	Joe Perches <joe@...ches.com>,
	"David S. Miller" <davem@...emloft.net>,
	Stephen Warren <swarren@...dia.com>,
	Arnd Bergmann <arnd@...db.de>,
	David Brown <davidb@...eaurora.org>,
	Dom Cobley <popcornmix@...il.com>
Subject: Re: [RFC PATCH] fpga: Introduce new fpga subsystem

On Mon, Sep 23, 2013 at 03:10:11PM +0200, Michal Simek wrote:

> > 1) The driver doesn't know what firmware to request. It just knows
> >    how to send it to a FPGA.
> 
> But dts property in the manager driver which uses this as end driver
> can know that.

I think the device tree maintainers would push back on this since it
is not "describing the hardware"
 
> > 2) Telling the kernel a filename via sysfs and then having it go
> >    around the long way via request_firwmare to get the data is silly.
> >    Just give the kernel the actual data instead of a file name
> 
> Firmware interface is valid way how to pass bitstream to the kernel.
> If you don't like just don't use it. For example you can add
> firmware blob directly to the kernel and load this at bootup phase
> without user-space access.

I'm not against using request firmware for what it is ment for: having
the kernel autonomously load firmware.

I am against the sysfs API in the core code where userspace writes a
file name that is then used to request_firwmare. That is a goofy API
for the reasons I outlined.

It is appropriate to use request firmware at the driver level where
the driver somehow knows what FPGA to request.

> and there will be this option. But don't try to restrict others
> if they want to do it just in the kernel in early phase.

Doing the load in kernel early phase doesn't involve the user space
sysfs interface.

Jason
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