On Fri, Feb 8, 2013 at 5:28 PM, Arnd Bergmann <a...@arndb.de> wrote: > On Friday 08 February 2013 16:22:48 Russell King - ARM Linux wrote: >> If it's DMA _to_ a device, then we will only ever clean the lines prior to >> a transfer, never invalidate them. So that's not really a concern. (There >> better not be any dirty cache lines associated with the empty zero page >> either.) > > Right, makes sense. I thought I had read about a CPU that > could not flush a cache line without also invalidating > it, but that must have been something other than ARM, > or maybe I'm misremembering it.
I don't think it matters one bit. The page can contain a bitmap of Donald Duck or zero FWIW. It's just that the DMA controller just neeeds to read *something* that does not cause a bus stall. It's due to the syncronous nature of the SPI protocol, to get something out you need to put something in. So when reading, this is a way to feed in some junk. So this goes on my TODO... Yours, Linus Walleij ------------------------------------------------------------------------------ Free Next-Gen Firewall Hardware Offer Buy your Sophos next-gen firewall before the end March 2013 and get the hardware for free! Learn more. http://p.sf.net/sfu/sophos-d2d-feb _______________________________________________ spi-devel-general mailing list spi-devel-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/spi-devel-general
