From patchwork Fri Jun 17 22:45:12 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Franklin Cooper X-Patchwork-Id: 9185099 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id C29596075F for ; Fri, 17 Jun 2016 22:46:14 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B1C1227EE2 for ; Fri, 17 Jun 2016 22:46:14 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id A433528236; Fri, 17 Jun 2016 22:46:14 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 0E22B27EE2 for ; Fri, 17 Jun 2016 22:46:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932459AbcFQWpo (ORCPT ); Fri, 17 Jun 2016 18:45:44 -0400 Received: from arroyo.ext.ti.com ([198.47.19.12]:60396 "EHLO arroyo.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932412AbcFQWpm (ORCPT ); Fri, 17 Jun 2016 18:45:42 -0400 Received: from dlelxv90.itg.ti.com ([172.17.2.17]) by arroyo.ext.ti.com (8.13.7/8.13.7) with ESMTP id u5HMjaoK015073; Fri, 17 Jun 2016 17:45:36 -0500 Received: from DFLE72.ent.ti.com (dfle72.ent.ti.com [128.247.5.109]) by dlelxv90.itg.ti.com (8.14.3/8.13.8) with ESMTP id u5HMjaFb019086; Fri, 17 Jun 2016 17:45:36 -0500 Received: from dlep32.itg.ti.com (157.170.170.100) by DFLE72.ent.ti.com (128.247.5.109) with Microsoft SMTP Server id 14.3.294.0; Fri, 17 Jun 2016 17:45:35 -0500 Received: from dbdmail01.india.ti.com (dbdmail01.india.ti.com [172.24.162.206]) by dlep32.itg.ti.com (8.14.3/8.13.8) with ESMTP id u5HMjYjT006956; Fri, 17 Jun 2016 17:45:35 -0500 Received: from udb0273011.am.dhcp.ti.com (udb0273011.am.dhcp.ti.com [128.247.83.33]) by dbdmail01.india.ti.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id u5HMjN1N006459; Sat, 18 Jun 2016 04:15:31 +0530 From: Franklin S Cooper Jr To: , , , , , , , CC: Franklin S Cooper Jr Subject: [RFC] [PATCH 2/3] spi: omap2-mcspi: Add comments for RX only DMA buffer workaround Date: Fri, 17 Jun 2016 17:45:12 -0500 Message-ID: <1466203513-4771-3-git-send-email-fcooper@ti.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1466203513-4771-1-git-send-email-fcooper@ti.com> References: <1466203513-4771-1-git-send-email-fcooper@ti.com> MIME-Version: 1.0 Sender: linux-spi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-spi@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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;