linux-kernel - Re: [RFC] dma-buf: Implement test module

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Message-ID: <20140711203323.GA10328@ravnborg.org>
Date:	Fri, 11 Jul 2014 22:33:23 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
	linux-kernel@...r.kernel.org, Michal Marek <mmarek@...e.cz>,
	linux-kbuild@...r.kernel.org
Subject: Re: [RFC] dma-buf: Implement test module

On Thu, Jul 10, 2014 at 11:55:26AM +0200, Thierry Reding wrote:
> On Wed, Mar 26, 2014 at 09:32:47AM +0100, Thierry Reding wrote:
> > On Tue, Mar 25, 2014 at 07:01:10PM +0100, Sam Ravnborg wrote:
> > > > 
> > > > There are two things that don't work too well with this. First this
> > > > causes the build to break if the build machine doesn't have the new
> > > > public header (include/uapi/linux/dma-buf.h) installed yet. So the only
> > > > way to make this work would be by building the kernel once with SAMPLES
> > > > disabled, install the headers and then build again with SAMPLES enabled.
> > > > Which really isn't very nice.
> > > > 
> > > > One other option that I've tried is to modify the include path so that
> > > > the test program would get the in-tree copy of the public header file,
> > > > but that didn't build properly either because the header files aren't
> > > > properly sanitized and therefore the compiler complains about it
> > > > (include/uapi/linux/types.h).
> > > > 
> > > > One other disadvantage of carrying the sample program in the tree is
> > > > that there's only infrastructure to build programs natively on the build
> > > > machine. That's somewhat unfortunate because if you want to run the test
> > > > program on a different architecture you have to either compile the
> > > > kernel natively on that architecture (which isn't very practical on many
> > > > embedded devices) or cross-compile manually.
> > > > 
> > > > I think a much nicer solution would be to add infrastructure to cross-
> > > > compile these test programs, so that they end up being built for the
> > > > same architecture as the kernel image (i.e. using CROSS_COMPILE).
> > > > 
> > > > Adding Michal and the linux-kbuild mailing list, perhaps this has been
> > > > discussed before, or maybe somebody has a better idea on how to solve
> > > > this.
> > > I actually looked into this some time ago.
> > > May try to dust off the patch.
> > > IIRC the kernel provided headers were used for building - not the one installed on the machine.
> > > And crosscompile were supported.
> > 
> > That sounds exactly like what I'd want for this. If you need any help,
> > please let me know.
> 
> Did you have any time to look into dusting off the patch? If not I'll
> gladly take whatever you have and dust it off myself.
Thanks for the reminder.
I got it almost working after simplifying it a lot.
I will be travelling for the next few days but will continue to work on this
after the weekend.

	Sam
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