From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <46815286.1010808@de.ibm.com> Date: Tue, 26 Jun 2007 19:53:10 +0200 From: Carsten Otte MIME-Version: 1.0 To: Arnd Bergmann Subject: Re: [Cbe-oss-dev] [patch 3/5] cell: updated driver for DDR2 memory on AXON References: <200706261821.06516.arnd@arndb.de> In-Reply-To: <200706261821.06516.arnd@arndb.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: Maxim Shchetynin , linuxppc-dev@ozlabs.org, cbe-oss-dev@ozlabs.org Reply-To: carsteno@de.ibm.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Arnd Bergmann wrote: > What will actually happen if you try to mount an axonram device with ext2? > I suppose mount should fail with a proper error code if the block size is > larger than 4kb, but does that happen? > > If you have a 4k block size axonram device, the ext2 really should work > using XIP as expected, including the mmap() operation. > Absolutely. What's the symptom if you try mount -o xip? I am willing to fix any bugs that show in the ext2/xip code in that scenario... >> We have the direct_access method here only because it is needed for the >> azfs file-system, which we recommend to use for accessing the Axon's RAM >> rather then ext2 or any other buffered file-systems. > > I think I've understood what the problem is now. The generic xip code > assumes that the data to be mapped has a 'struct page' in mem_map, > and that it's part of the linear kernel mapping. This is actually > true on s390, where it is currently used, but not for us. The point > on s390 is that the kernel virtual address is _identical_ to the > physical address, so it may never have shown up as a problem. > > I'll talk to Carsten about this, he already had plans to remove > the need for struct page from the filemap_xip infrastructure. Removing the need for struct page is indeed impossible with current memory management because of the fact that VM_PFNMAP vmas have the downside that they require a linear physical image of the vma. Ext2 does not comply to that requriement, a given file may be spread all over a media.