From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Date: Mon, 14 Dec 2015 08:48:16 +0100 Subject: [U-Boot] ARMv7 MMU shareability issue In-Reply-To: <20151214082519.37a17ddc@lilith> References: <1449582222-6506-1-git-send-email-marex@denx.de> <201512091509.13227.marex@denx.de> <20151210022708.GR667@bill-the-cat> <201512100453.01143.marex@denx.de> <20151214082519.37a17ddc@lilith> Message-ID: <20151214074815.GA16903@amd> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hi! > This patch has several effects: > > - it selects proper ARMv7 translation table level 1 bit definitions; > - it provides proper ARMv7 definitions for WT/WB/WA; > - it selects proper ARMv7 settings for TTBR0. > > All these are correct as per the docs I have (although I may have missed > something during the readings (and cross-readings with Marek) of these > last hours/days. > > Now, one specific effect goes against performance, and it is the > setting of bit S in all TT entries. This bit makes the corresponding > region shareable, but for all I know, in U-Boot we don't have more than > one core accessing the same memory or registers sets so -- at least for > the major part of its execution -- there is no reason for any region to > be shareable. Well, I'm currently working on AMP patch, which will mean two processors at the same time in u-boot. Also... we provide memory modify operations for the user. User may be trying to communicate with second core. > /That/ effect I certainly don't want. How big is the slowdown from S bit? Best regards, Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html