From mboxrd@z Thu Jan 1 00:00:00 1970 From: Reinhard Meyer Date: Fri, 05 Aug 2011 11:23:28 +0000 Subject: [U-Boot] [PATCH v2] ARM926ejs: Add routines to invalidate D-Cache In-Reply-To: <4E3BCDEB.8090106@aribaud.net> References: <1312519452-22926-1-git-send-email-hong.xu@atmel.com> <4E3B8A16.50604@aribaud.net> <4E3B8FF3.2070400@atmel.com> <4E3B91C1.2040307@aribaud.net> <4E3B9753.3020002@ti.com> <4E3BC715.9070706@atmel.com> <4E3BCA55.5070003@ti.com> <4E3BCDEB.8090106@aribaud.net> Message-ID: <1312543408.31913.170.camel@ubuntu> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Dear Albert, Aneesh, Eric, > > We have a fundamental problem when it comes to invalidating an > > un-aligned buffer. Either you flush the boundary lines and corrupt your > > buffer at boundaries OR you invalidate without flushing and corrupt > > memory around your buffer. Both are not good! The only real solution is > > to have aligned buffers, if you want to have D-cache enabled and do DMA > > at the same time. > > Plus, there should not be *heavy* modifications; DMA engines tend to use > essentially two types of memory-resident objects: data buffers and > buffer descriptors. There's only a small handful of places in the driver > code to look at to find where these objects are allocated and how. > > So I stand by my opinion: since the cache invalidation routine should > only be called with cache-aligned objects, there is no requirement to > flush the first (resp. last) cache line in case of unaligned start > (resp.stop), and I don't want cache operations performed when they are > not required. After considering all issues, any driver that does flush OR invalidate a cache line that it does not fully "own" is prone to cause problems. At flushing: some DMA might just have put data into the partial line. At invalidating: some Software might have put data, but the writeback had not occured. So both flush AND invalidate functions should check for this event and emit a proper warning on the console. My 2.7 cents... Reinhard