From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Fri, 29 Jul 2011 12:05:25 +0100 Subject: [PATCH 10/18] dmaengine/amba-pl08x: Get rid of pl08x_pre_boundary() In-Reply-To: References: Message-ID: <20110729110525.GG25640@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.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.