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Date: Sat, 14 Nov 2015 11:02:58 +0100 From: Anton Bondarenko <anton.bondarenko.sama@...il.com> To: Sascha Hauer <s.hauer@...gutronix.de> Cc: broonie@...nel.org, b38343@...escale.com, linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, vladimir_zapolskiy@...tor.com, jiada_wang@...tor.com Subject: Re: [PATCH v3 1/7] spi: imx: Fix DMA transfer On 05.11.2015 17:51, Anton Bondarenko wrote: > On 05.11.2015 09:34, Sascha Hauer wrote: >> On Sun, Nov 01, 2015 at 03:41:35PM +0100, Anton Bondarenko wrote: >>> From: Anton Bondarenko <anton_bondarenko@...tor.com> >>> >>> 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 >> > > A lot of times. Current implementation is trying to use it, but works > incorrectly if length % WML != 0 (which means RX_DMA_LENGTH == 0). > > Regards, Anton Does anyone has other comments regarding this commit? Regards, Anton -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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