On Mon, Jan 27, 2014 at 04:13:56PM +0100, Guennadi Liakhovetski wrote: > Hi all, > > I'm working on an MMC driver with a DMA capability. All has been working > well, until at some point I've got a bus error, when the mmc driver had > been handed in a buffer at 0x3000 physical RAM address. The reason is, > that on Zynq arch bus masters cannot access RAM below 0x80000. Therefore > my question: how shall I configure this in software? > > The way I found was to use ARM-specific struct dmabounce_device_info and > implement its .needs_bounce() method to return true for those addresses. > Is this the right way or is there a better / more straight-forward one? > > To do the above I have to enable CONFIG_DMABOUNCE, which then selects > CONFIG_ZONE_DMA. Having done just that I suddenly discover, that 0x3000 > buffers aren't used any more, so, I cannot actually verify my > implementation :) Looking at ZONE_DMA it looks like it is still covering > the whole RAM range (/proc/zoneinfo shows start_pfn=0 in zone DMA), so, I > don't see why 0x3000 should be excluded now. > > So, is using the .needs_bounce() method the correct way to support DMA on > this arch or is there a better one? I have a similar issue with Renesas R8A7790 where there is a bus bridge that can only deal with transactions to one half of the available RAM. -- Ben Dooks, ben@xxxxxxxxx, http://www.fluff.org/ben/ Large Hadron Colada: A large Pina Colada that makes the universe disappear. -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
