From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932112Ab1G2LFn (ORCPT ); Fri, 29 Jul 2011 07:05:43 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:50798 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756090Ab1G2LFm (ORCPT ); Fri, 29 Jul 2011 07:05:42 -0400 Date: Fri, 29 Jul 2011 12:05:25 +0100 From: Russell King - ARM Linux To: Viresh Kumar Cc: linus.walleij@linaro.org, pratyush.anand@st.com, rajeev-dlh.kumar@st.com, bhupesh.sharma@st.com, shiraz.hashim@st.com, vinod.koul@intel.com, linux-kernel@vger.kernel.org, vipin.kumar@st.com, armando.visconti@st.com, amit.virdi@st.com, vipulkumar.samar@st.com, viresh.linux@gmail.com, deepak.sikri@st.com, dan.j.williams@intel.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 10/18] dmaengine/amba-pl08x: Get rid of pl08x_pre_boundary() Message-ID: <20110729110525.GG25640@n2100.arm.linux.org.uk> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 29, 2011 at 04:19:20PM +0530, Viresh Kumar wrote: > Pl080 Manual says: "Bursts do not cross the 1KB address boundary" > > We can program the controller to cross 1 KB boundary on a burst and controller > can take care of this boundary condition by itself. > > Following is the discussion with ARM Technical Support Guys (David): > [Viresh] Manual says: "Bursts do not cross the 1KB address boundary" > > What does that actually mean? As, Maximum size transferable with a single LLI is > 4095 * 4 =16380 ~ 16KB. So, if we don't have src/dest address aligned to burst > size, we can't use this big of an LLI. > > [David] There is a difference between bursts describing the total data > transferred by the DMA controller and AHB bursts. Bursts described by the > programmable parameters in the PL080 have no direct connection with the bursts > that are seen on the AHB bus. > > The statement that "Bursts do not cross the 1KB address boundary" in the TRM is > referring to AHB bursts, where this limitation is a requirement of the AHB spec. > You can still issue bursts within the PL080 that are in excess o f 1KB. The > PL080 will make sure that its bursts are broken down into legal AHB bursts which > will be formatted to ensure that no AHB burst crosses a 1KB boundary. > > Based on above discussion, this patch removes all code related to 1 KB boundary > as we are not required to handle this in driver. Good. I'm glad someone's finally getting to the bottom of what's actually required and what isn't... This driver has been a mess for quite a long time and is in desperate need of these kinds of cleanups.