From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sascha Hauer Subject: Re: [PATCH v3 1/7] spi: imx: Fix DMA transfer Date: Thu, 5 Nov 2015 09:34:22 +0100 Message-ID: <20151105083422.GH8526@pengutronix.de> References: <1446388901-6073-1-git-send-email-anton.bondarenko.sama@gmail.com> <1446388901-6073-2-git-send-email-anton.bondarenko.sama@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: broonie@kernel.org, b38343@freescale.com, linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, vladimir_zapolskiy@mentor.com, jiada_wang@mentor.com To: Anton Bondarenko Return-path: Content-Disposition: inline In-Reply-To: <1446388901-6073-2-git-send-email-anton.bondarenko.sama@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-spi.vger.kernel.org On Sun, Nov 01, 2015 at 03:41:35PM +0100, Anton Bondarenko wrote: > From: Anton Bondarenko > > RX DMA tail data handling doesn't work correctly in many cases with > current implementation. It happens because SPI core was setup > to generates both RX watermark level and RX DATA TAIL events > incorrectly. SPI transfer triggering for DMA also done in wrong way. > > SPI client wants to transfer 70 words for example. The old DMA > implementation setup RX DATA TAIL equal 6 words. In this case > RX DMA event will be generated after 6 words read from RX FIFO. > The garbage can be read out from RX FIFO because SPI HW does > not receive all required words to trigger RX watermark event. > > New implementation change handling of RX data tail. DMA is used to process > all TX data and only full chunks of RX data with size aligned to FIFO/2. > Driver is waiting until both TX and RX DMA transaction done and all > TX data are pushed out. At that moment there is only RX data tail in > the RX FIFO. This data read out using PIO. Have you looked at the RX_DMA_LENGTH and RXTDEN fields of the DMA register? These seem to be for handling the remaining bytes of a DMA transfer which do not reach the watermark level. From reading the documentation I haven't really understood how it works though. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |