On Mon, Nov 09, 2015 at 11:29:17AM +0530, sanjeev sharma wrote: > On Wed, Nov 04, 2015 at 10:39:13AM +0000, Will Deacon wrote: > > On Wed, Nov 04, 2015 at 03:26:48PM +0530, Sanjeev Sharma wrote: > > > _dma_page_cpu_to_dev() treat DMA_BIDIRECTIONAL similar to > > > DMA_TO_DEVICE which means that destination buffer is device > > > memory,means cpu may have written some data to source buffer and > > > data may be in cache line.For cleaner operation we need to call > > > outer_flush_range() which will clean and invalidate outer cache lines. > > > > Why isn't the clean sufficient in this case? We're mapping the buffer > > to the device, so we clean the dirty lines in the CPU caches and make > > them visible to the device. If the CPU later wants to read the buffer > > (i.e. after the device has DMA'd into it), you'll need to map the > > buffer to the CPU, which will perform the invalidation of the CPU > caches. > > Indeed. bidirectional mode is already handled prefectly well by this > code. No patches are required. > > Thanks Russell & Will for providing input. > > Let's assume , CPU don't read the buffer then there could be the problem > correct ? IMO, to handle every use case outer_flush_range can be used ? > If still it doesn't make sense to use flush on bidirectional mappings, > then > FIXME comment should be removed from the function to avoid any > Confusion. > > > > Please let me know what you think on above comment ?
I still don't understand the problem that you're trying to fix. Sorry, Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
