From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Airlie Subject: Re: [PATCH] drm: Compare only lower 32 bits of framebuffer map offsets Date: Mon, 30 May 2011 09:29:04 +1000 Message-ID: <1306711744.21613.14.camel@clockmaker-el6> References: <1306710750-31992-1-git-send-email-lists.tormod@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by gabe.freedesktop.org (Postfix) with ESMTP id 49DF59E754 for ; Sun, 29 May 2011 16:29:08 -0700 (PDT) In-Reply-To: <1306710750-31992-1-git-send-email-lists.tormod@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org Errors-To: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org To: Tormod Volden Cc: dri-devel@lists.freedesktop.org List-Id: dri-devel@lists.freedesktop.org On Mon, 2011-05-30 at 01:12 +0200, Tormod Volden wrote: > From: Tormod Volden > > Drivers using multiple framebuffers got broken by commit > 41c2e75e60200a860a74b7c84a6375c105e7437f which ignored the framebuffer > (or register) map offset when looking for existing maps. The rationale > was that the kernel-userspace ABI is fixed at a 32-bit offset, so the > real offsets could not always be handed over for comparison. > > Instead of ignoring the offset we will compare the lower 32 bit. Drivers > using multiple framebuffers should just make sure that the lower 32 bit > are different. The existing drivers in question are practically limited > to 32-bit systems so that should be fine for them. > > It is assumed that current drivers always specify a correct framebuffer > map offset, even if this offset was ignored since above commit. So this > patch should not change anything for drivers using only one framebuffer. > > Drivers needing multiple framebuffers with 64-bit map offsets will need > to cook up something, for instance keeping an ID in the lower bits, > which is to be aligned away when it comes to using the offset. > > Signed-off-by: Tormod Volden > --- > > What about this idea? (Untested patch) If you test it and it works I like it best. Simple and clear, and pretty close to what I was thinking was a good idea. As you say if someone needs this functionality in a new driver they can fix it, but really new drivers shouldn't be doing anything in this area. Dave.