From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sceptre.pobox.com (sceptre.pobox.com [207.106.133.20]) by ozlabs.org (Postfix) with ESMTP id 04809DDE32 for ; Thu, 9 Aug 2007 14:16:50 +1000 (EST) Date: Wed, 8 Aug 2007 23:16:32 -0500 From: Nathan Lynch To: David Gibson Subject: Re: [RFC/PATCH] remove gratuitous reads from maple pci config space methods Message-ID: <20070809041632.GA13921@localdomain> References: <20070809005044.GD10114@localdomain> <20070809030555.GA8261@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20070809030555.GA8261@localhost.localdomain> Cc: linuxppc-dev@ozlabs.org, Paul Mackerras List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , David Gibson wrote: > On Wed, Aug 08, 2007 at 07:50:44PM -0500, Nathan Lynch wrote: > > The maple pci configuration space write methods read the written > > location immediately after the write is performed, presumably in order > > to flush the write. However, configuration space writes are not > > allowed to be posted, making these reads gratuitous. > > It might be worth checking that there isn't a particular reason for > these. Just because posting writes are forbidden doesn't mean a > particular bridge won't screw it up... Well, I had already checked with Ben, who wrote the code, and my understanding is that the reads are intended to work around some misbehaving Apple bridges, but that a sync after the write (implied by releasing pci_lock in the generic pci code) should suffice for those.