On Thu, 2010-03-04 at 16:30 +0000, Russell King - ARM Linux wrote: > On Fri, Mar 05, 2010 at 12:41:03AM +0900, Paul Mundt wrote: > > On Thu, Mar 04, 2010 at 03:29:38PM +0000, Catalin Marinas wrote: > > > On Thu, 2010-03-04 at 14:21 +0000, James Bottomley wrote: > > > > The thing which was discovered in this thread is basically that ARM is > > > > handling deferred flushing (for D/I coherency) in a slightly different > > > > way from everyone else ... > > > > > > Doing a grep for PG_dcache_dirty defined in terms of PG_arch_1 reveals > > > that MIPS, Parisc, Score, SH and SPARC do similar things to ARM. PowerPC > > > and IA-64 use PG_arch_1 as a clean rather than dirty bit. > > > > SH used to use it as a PG_mapped which was roughly similar to the > > PG_dcache_clean approach, at which point things like flushing for the PIO > > case in the HCD wasn't necessary. It did result in rather aggressive over > > flushing though, which is one of the reasons we elected to switch to > > PG_dcache_dirty. > > > > Note that the PG_dcache_dirty semantics are also outlined in > > Documentation/cachetlb.txt for PG_arch_1 usage, so it's hardly esoteric. > > Indeed; the ARM approach was basically taken from Sparc64. [...] > The general critera (from memory) seems to be: > - a virtual indexed aliasing cache (whether it be VIVT or VIPT aliasing) > - write allocate caches show the problem better than read allocate only > - using a block device for the filesystem > - mmap'ing a page and immediately accessing the last few cache lines in > that page It actually triggers easily with a non-aliasing VIPT cache (can't even start /sbin/init). The main condition is for the caches to be in write-allocate mode (and the processor to support this, i.e. Cortex-A9). A simple test is to use an ext2/3 filesystem (cramfs, jffs2 etc. wouldn't do since they call flush_dcache_page) on a compact flash card using the pata_platform driver (and without commit 2d68b7fe55d9e19). Other forms of triggering this is to use something like slram + ext2/3. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
