Messages in this thread | | | Subject | Re: [PATCH v3 1/7] spi: imx: Fix DMA transfer | From | Anton Bondarenko <> | Date | Thu, 5 Nov 2015 17:51:09 +0100 |
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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@mentor.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
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