From mboxrd@z Thu Jan 1 00:00:00 1970 From: Albert ARIBAUD Date: Wed, 10 Jul 2013 14:30:30 +0200 Subject: [U-Boot] [RFC PATCH] arm: arm926ejs: flush cache before disable it In-Reply-To: <20130710100510.GB2450@Hardy> References: <1372768555-12477-1-git-send-email-voice.shen@gmail.com> <20130705230200.5c64c39c@lilith> <51D9FABE.7000705@gmail.com> <20130708122257.5f0100ec@lilith> <20130708120846.GA4824@Hardy> <20130708143216.22906bf7@lilith> <20130708140722.GA6642@Hardy> <20130708215551.1c16cb06@lilith> <20130709061134.GA3176@Hardy> <20130709102813.63de0b18@lilith> <20130710100510.GB2450@Hardy> Message-ID: <20130710143030.37221f93@lilith> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hi Sughosh, On Wed, 10 Jul 2013 15:35:10 +0530, Sughosh Ganu wrote: > hi Albert, > > On Tue Jul 09, 2013 at 10:28:13AM +0200, Albert ARIBAUD wrote: > > > > > The arm926ej-s data cache does not have a single fixed policy, and > > > > does not have a bypass-on-write policy, only write-through and > > > > copy-back. > > > > > > > > Other, more complex, policies may be defined, but at the MMU, not cache, > > > > level, and those are not constant for all arm926ej-s based SoCs; not > > > > even constant for a given SoC as they are configurable at run-time to > > > > fit the chosen system addressing map. > > > > > > Can you please elucidate on these policies. Based on my reading of the > > > arm developers manual and the arm926ejs trm, the mmu makes a > > > particular region cacheable and/or write bufferable. I did not find > > > mention of any other policies. Maybe pointers or links to the > > > documents would help. > > > > You are correct re the other policies of the DDI0198E (ARM926EJ-S > > TRM) MMU -- page 3-11, bits 3-2 of the section descriptor. Note however > > that you may have to refer to your specific SoC's TRM or equivalent, as > > the SoC designer may have defined its own system-level cache and MMU > > architecture. > > > > Note in any case that none of the policies mentioned in DDI0198E is > > described as read-allocate (let alone "read-allocate only" where writes > > would bypass the enabled cache); on the contrary, the only cache > > policies mentioned are write-through and write-back, both of which > > contradict cache bypass on write. > > I was referring to the cache allocation policy mentioned in section > 4.1 in the DDI0198E document -- this is also mentioned in table 12.1 > in chapter 12 of the arm developers guide. Can you please quote the exact part of 4.1 which describes the cache policy and then explain what you think it means exactly? > -sughosh Amicalement, -- Albert.