From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ben Widawsky <ben@bwidawsk.net>
Subject: Re: [PATCH] drm/i915: Dumb down the semaphore logic
Date: Fri, 2 Sep 2011 14:02:54 +0000
Message-ID: <20110902140254.GA30736@cloud01>
References: <1314935735-5451-1-git-send-email-ben@bwidawsk.net>
	<d08817$1asrm7@azsmga001.ch.intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org>
Received: from cloud01.chad-versace.us (184-106-247-128.static.cloud-ips.com
	[184.106.247.128])
	by gabe.freedesktop.org (Postfix) with ESMTP id 8744AA15CC
	for <intel-gfx@lists.freedesktop.org>;
	Fri,  2 Sep 2011 06:59:51 -0700 (PDT)
Content-Disposition: inline
In-Reply-To: <d08817$1asrm7@azsmga001.ch.intel.com>
List-Unsubscribe: <http://lists.freedesktop.org/mailman/options/intel-gfx>,
	<mailto:intel-gfx-request@lists.freedesktop.org?subject=unsubscribe>
List-Archive: <http://lists.freedesktop.org/archives/intel-gfx>
List-Post: <mailto:intel-gfx@lists.freedesktop.org>
List-Help: <mailto:intel-gfx-request@lists.freedesktop.org?subject=help>
List-Subscribe: <http://lists.freedesktop.org/mailman/listinfo/intel-gfx>,
	<mailto:intel-gfx-request@lists.freedesktop.org?subject=subscribe>
Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org
Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: intel-gfx@lists.freedesktop.org
List-Id: intel-gfx@lists.freedesktop.org

On Fri, Sep 02, 2011 at 09:54:32AM +0100, Chris Wilson wrote:
> On Thu,  1 Sep 2011 20:55:35 -0700, Ben Widawsky <ben@bwidawsk.net> wrote:
> > While I think the previous code is correct, it was hard to follow and
> > hard to debug. Since we already have a ring abstraction, might as well
> > use it to handle the semaphore updates and compares.
> > 
> > I don't expect this code to make semaphores better or worse, but you
> > never know...
> 
> So "dumbing it down" means using macros instead of small functions and
> putting magic values into the ring structure. I'm not sure if that's an
> improvement to readability at all.
> -Chris

The previous code for doing an update was non obvious to me. Obviously I
will be biased in thinking my code is easier to follow, but for the
existing code I had to map out exactly what it's doing every single time
I went through it to convince myself it is correct.

Using pointer arithmetic and then RING_SYNC_0 with math did not seem the
correct way to do it. As for the magic values, they started out as
non-magic, but got changed at some point during developing the patch. At
the end I went back to magic to reduce the LOC.  You'll notice the
comments there make them slightly less magic.

And although a lame argument... if a new ring comes along the previous code was
not very well equiped to handle it.

Ben