-----Original Message----- From: Russell King - ARM Linux [mailto:li...@arm.linux.org.uk] Sent: Wednesday, November 04, 2015 4:24 PM To: Will Deacon Cc: Sharma, Sanjeev; m.szyprow...@samsung.com; linux-arm-ker...@lists.infradead.org; linux-kernel@vger.kernel.org Subject: Re: [PATCH] ARM:dma-mapping: Handle DMA_BIDIRECTIONAL in _dma_page_cpu_to_dev()
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. (I never received the original email.) -- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
