From mboxrd@z Thu Jan 1 00:00:00 1970 From: marek.vasut@gmail.com (Marek Vasut) Date: Sat, 19 Feb 2011 21:22:53 +0100 Subject: Question About Linux Memory Mapping In-Reply-To: References: Message-ID: <201102192122.53746.marek.vasut@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Friday 18 February 2011 21:56:28 Drasko DRASKOVIC wrote: > Hi all, > in the article Booting ARM Linux : > http://www.simtec.co.uk/products/SWLINUX/files/booting_article.html > I can see that mem map is passed via ATAG_MEM. However, in the same > article it is mentioned that this information can also be passed via > kernel command line paramters, mem=[KM][,@]. > > However, this does not seem to be true, as "mem" command line > parameter seems to be formated like this : mem= n[KMG] (i.e. no > offset), regarding to this reference : > http://oreilly.com/linux/excerpts/9780596100797/kernel-boot-command-line-pa > rameter-reference.html. Seems like memmap should be used instead. > > I tried passing the parameters like memmap= n[KMG]@start[KMG] but that > had no effect at all - still the same amount of System Ram was read > from ATAGS and presented in the system via /proc/iomem. > > What I needed it to reserve 1MB region for one FIFO at the end of RAM > (or somewhere else) > and protect it from the kernel. I tried passing memmap= > n[KMG]$start[KMG], but that did not worn neither. What are you exactly trying to achieve ? btw. if you really need to make a hole in RAM, you should reserve a bootmem node maybe? > > So my questions are following : > 1) Why commandlines are ignored and ATAGS are given priority ? > 2) What is the most elegant way to protect one region in RAM : > a) By giving less memory with ATAGS_MEM and thus making protected > region invisible to Linux, lying to it that RAM is smaller > b) By changing somehow linker script > c) By changing some configuration variables (which ?) > > Thanks for the answers and best regards, > Drasko > > _______________________________________________ > linux-arm mailing list > linux-arm at lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm