Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755667Ab3JHKp1 (ORCPT ); Tue, 8 Oct 2013 06:45:27 -0400 Received: from mail-la0-f52.google.com ([209.85.215.52]:61758 "EHLO mail-la0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756611Ab3JHKoi (ORCPT ); Tue, 8 Oct 2013 06:44:38 -0400 MIME-Version: 1.0 From: Richard Genoud Date: Tue, 8 Oct 2013 12:44:16 +0200 Message-ID: Subject: [BUG] spi/spi-atmel: DMA rx buffer corruption with SPI_IOC_MESSAGE To: Nicolas Ferre , Mark Brown , Wenyou Yang Cc: linux-spi@vger.kernel.org, "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1741 Lines: 52 Hi all, I finally found the bug I saw months ago, before "[PATCH v8 3/8] spi/spi-atmel: add dmaengine support" was merged. Here it is: When the ioctl SPI_IOC_MESSAGE is used with small and big buffers, the big RX buffer is corrupted with bytes from the big TX buffer. (Small means size < DMA_MIN_BYTES, Big means size > DMA_MIN_BYTES) I'm attaching the test software that I used ( ./spi_test /dev/spidevx.x ) It fills 3 TX buffers with 0xAA pattern: a small, a big and a small again. It reads in return 3 RX buffers. The MISO pin has to be on 3.3v. It checks if the received buffers are filled with 0xFF (they should be, as MISO is high). And I've got a lot of buffers filled partially with 0xAA bytes. BUT, if you apply this patch: ---8<---- diff --git a/drivers/spi/spi-atmel.c b/drivers/spi/spi-atmel.c index 83cf609..cde42a4 100644 --- a/drivers/spi/spi-atmel.c +++ b/drivers/spi/spi-atmel.c @@ -187,7 +187,7 @@ /* use PIO for small transfers, avoiding DMA setup/teardown overhead and * cache operations; better heuristics consider wordsize and bitrate. */ -#define DMA_MIN_BYTES 16 +#define DMA_MIN_BYTES 0 struct atmel_spi_dma { struct dma_chan *chan_rx; ---8<---- There's no error any more. So there's something wrong happening when switching from/to pio transfer to/from DMA. We didn't saw that at the time of the merge because we did the test with a loop on MISO/MOSI, so the RX buffer was corrupted with identical bytes. Best regards, Richard. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/