From mboxrd@z Thu Jan 1 00:00:00 1970 From: karl.beldan@gmail.com (Karl Beldan) Date: Tue, 31 Jul 2012 10:30:22 +0200 Subject: About dma_sync_single_for_{cpu,device} In-Reply-To: <50178A69.8050906@ladisch.de> References: <20120730202401.GA4947@gobelin> <20120731064557.GA4676@gobelin> <50178249.7090306@ladisch.de> <50178A69.8050906@ladisch.de> Message-ID: <20120731083022.GA5026@ed-laptop> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Jul 31, 2012 at 09:34:01AM +0200, Clemens Ladisch wrote: > Karl Beldan wrote: > > On 7/31/12, Clemens Ladisch wrote: > >> Karl Beldan wrote: > >>> To tx a chunk of data from the SoC => network device, we : > >>> - prepare a buffer with a leading header embedding a pattern, > >>> - trigger the xfer and wait for an irq > >>> // The device updates the pattern and then triggers an irq > >>> - upon irq we check the pattern for the xfer completion > >>> > >>> I was expecting the following to work: > >>> addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); > >> > >> Of both the CPU and the device write to the buffer, you must use > >> DMA_BIDIRECTIONAL. > > > > This does not work (tested) : seems to me BIDIRECTIONAL would just > > add invalidate, and invalidate before the ram has been updated, as > > stated, does not work. > > Please show the exact sequence of dma_* calls, and also show when and > how the CPU and the device access the buffer. > Hmm, so I just spotted a line where we peek in the buffer after invalidating .. cannot believe I missed it .. so sorry for the noise .. now it's working. I felt I would find the culprit right after posting ;) Thanks Clemens !