From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751919AbcF0Oyq (ORCPT ); Mon, 27 Jun 2016 10:54:46 -0400 Received: from mail-oi0-f67.google.com ([209.85.218.67]:33568 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751981AbcF0OyO (ORCPT ); Mon, 27 Jun 2016 10:54:14 -0400 From: Franklin S Cooper Jr To: david.s.gordon@intel.com, axboe@fb.com, akpm@linux-foundation.org, ming.l@ssi.samsung.com, linux-kernel@vger.kernel.org, broonie@kernel.org, linux-spi@vger.kernel.org, nsekhar@ti.com, peter.ujfalusi@ti.com Cc: Franklin S Cooper Jr Subject: [RFC] [PATCH v2 2/3] spi: omap2-mcspi: Add comments for RX only DMA buffer workaround Date: Mon, 27 Jun 2016 09:54:08 -0500 Message-Id: <1467039249-7816-3-git-send-email-fcooper@ti.com> X-Mailer: git-send-email 2.7.0 In-Reply-To: <1467039249-7816-1-git-send-email-fcooper@ti.com> References: <1467039249-7816-1-git-send-email-fcooper@ti.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org OMAP35x and OMAP37x mentions in the McSPI End-of-Transfer Sequences section that if the McSPI is configured as a Master and only DMA RX is being performed then the DMA transfer size needs to be reduced by 1 or 2. This was originally implemented by: commit 57c5c28dbc83 ("spi: omap2_mcspi rxdma bugfix") This patch adds comments to clarify what is going on in the code since its not obvious what problem its addressing. Signed-off-by: Franklin S Cooper Jr --- drivers/spi/spi-omap2-mcspi.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/drivers/spi/spi-omap2-mcspi.c b/drivers/spi/spi-omap2-mcspi.c index 1d237e9..c47f958 100644 --- a/drivers/spi/spi-omap2-mcspi.c +++ b/drivers/spi/spi-omap2-mcspi.c @@ -459,6 +459,11 @@ omap2_mcspi_rx_dma(struct spi_device *spi, struct spi_transfer *xfer, count = xfer->len; dma_count = xfer->len; + /* + * In the "End-of-Transfer Procedure" section for DMA RX in OMAP35x TRM + * it mentions reducing DMA transfer length by one element in master + * normal mode. + */ if (mcspi->fifo_depth == 0) dma_count -= es; @@ -478,6 +483,10 @@ omap2_mcspi_rx_dma(struct spi_device *spi, struct spi_transfer *xfer, dmaengine_slave_config(mcspi_dma->dma_rx, &cfg); + /* + * Reduce DMA transfer length by one more if McSPI is + * configured in turbo mode. + */ if ((l & OMAP2_MCSPI_CHCONF_TURBO) && mcspi->fifo_depth == 0) dma_count -= es; @@ -507,6 +516,10 @@ omap2_mcspi_rx_dma(struct spi_device *spi, struct spi_transfer *xfer, if (mcspi->fifo_depth > 0) return count; + /* + * Due to the DMA transfer length reduction the missing bytes must + * be read manually to receive all of the expected data. + */ omap2_mcspi_set_enable(spi, 0); elements = element_count - 1; -- 2.7.0