From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= <ville.syrjala@linux.intel.com>
Subject: Re: [PATCH 2/2] drm/i915: Warn if ring tail is not
 qword aligned
Date: Mon, 26 Nov 2012 20:09:00 +0200
Message-ID: <20121126180900.GB21547@intel.com>
References: <1353934099-18685-1-git-send-email-ville.syrjala@linux.intel.com>
	<1353934099-18685-3-git-send-email-ville.syrjala@linux.intel.com>
	<453bf0$6k5283@azsmga001.ch.intel.com>
	<20121126174016.GB20128@intel.com>
	<eeac1e$54n7s8@AZSMGA002.ch.intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Return-path: <intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org>
Received: from mga03.intel.com (mga03.intel.com [143.182.124.21])
	by gabe.freedesktop.org (Postfix) with ESMTP id AE5EEE5D12
	for <intel-gfx@lists.freedesktop.org>;
	Mon, 26 Nov 2012 10:09:47 -0800 (PST)
Content-Disposition: inline
In-Reply-To: <eeac1e$54n7s8@AZSMGA002.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 Mon, Nov 26, 2012 at 05:46:48PM +0000, Chris Wilson wrote:
> On Mon, 26 Nov 2012 19:40:16 +0200, Ville Syrj=E4l=E4 <ville.syrjala@linu=
x.intel.com> wrote:
> > On Mon, Nov 26, 2012 at 04:25:47PM +0000, Chris Wilson wrote:
> > > On Mon, 26 Nov 2012 14:48:19 +0200, ville.syrjala@linux.intel.com wro=
te:
> > > > From: Ville Syrj=E4l=E4 <ville.syrjala@linux.intel.com>
> > > > =

> > > > Ringbuffer tail pointer must be qword aligned. Warn if someone
> > > > makes a mistake and forgets to pad the ring when the commands
> > > > inserted into the ring don't align to qword naturally.
> > > =

> > > The assertion should be that we wrote precisely the number of dwords =
we
> > > declared in intel_ring_begin(). Which is one of the important factors=
 to
> > > check whenever reviewing such code. This assertion (which should be a
> > > BUG_ON) is no substitute for such review.
> > =

> > Yeah. I was considering adding some reserved_space field to the ring,
> > populate it in ring_begin(), and and make sure it was correctly
> > consumed at ring_advance(). If you think that sounds good, I can cook
> > up a patch for it.
> =

> To be honest, I was thinking of a firing squad for the author and
> reviewers of any such patch that gets intel_ring_begin()..end() wrong.

I was mainly thinking it might helpful during development, to catch
obvious bugs. A compile time check would be even better though.

-- =

Ville Syrj=E4l=E4
Intel OTC