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[209.132.180.67]) by mx.google.com with ESMTP id om23si5601958ejb.194.2019.09.19.15.02.56; Thu, 19 Sep 2019 15:03:42 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390201AbfISO3s (ORCPT + 99 others); Thu, 19 Sep 2019 10:29:48 -0400 Received: from mx1.emlix.com ([188.40.240.192]:58610 "EHLO mx1.emlix.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727273AbfISO3r (ORCPT ); Thu, 19 Sep 2019 10:29:47 -0400 Received: from mailer.emlix.com (unknown [81.20.119.6]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.emlix.com (Postfix) with ESMTPS id 8F0D66036C; Thu, 19 Sep 2019 16:29:46 +0200 (CEST) From: Philipp Puschmann To: linux-kernel@vger.kernel.org Cc: yibin.gong@nxp.com, fugang.duan@nxp.com, l.stach@pengutronix.de, dan.j.williams@intel.com, vkoul@kernel.org, shawnguo@kernel.org, s.hauer@pengutronix.de, kernel@pengutronix.de, festevam@gmail.com, linux-imx@nxp.com, dmaengine@vger.kernel.or, linux-arm-kernel@lists.infradead.org, Philipp Puschmann Subject: [PATCH v4 2/3] dmaengine: imx-sdma: fix dma freezes Date: Thu, 19 Sep 2019 16:29:40 +0200 Message-Id: <20190919142942.12469-3-philipp.puschmann@emlix.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20190919142942.12469-1-philipp.puschmann@emlix.com> References: <20190919142942.12469-1-philipp.puschmann@emlix.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org For some years and since many kernel versions there are reports that the RX UART SDMA channel stops working at some point. The workaround was to disable DMA for RX. This commit tries to fix the problem itself. Due to its license i wasn't able to debug the sdma script itself but it somehow leads to blocking the scheduling of the channel script when a running sdma script does not find any free descriptor in the ring to put its data into. If we detect such a potential case we manually restart the channel. As sdmac->desc is constant we can move desc out of the loop. Fixes: 1ec1e82f2510 ("dmaengine: Add Freescale i.MX SDMA support") Signed-off-by: Philipp Puschmann Reviewed-by: Lucas Stach --- Changelog v4: - fixed the fixes tag Changelog v3: - use correct dma_wmb() instead of dma_wb() - add fixes tag Changelog v2: - clarify comment and commit description drivers/dma/imx-sdma.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c index e029a2443cfc..a32b5962630e 100644 --- a/drivers/dma/imx-sdma.c +++ b/drivers/dma/imx-sdma.c @@ -775,21 +775,23 @@ static void sdma_start_desc(struct sdma_channel *sdmac) static void sdma_update_channel_loop(struct sdma_channel *sdmac) { struct sdma_buffer_descriptor *bd; - int error = 0; - enum dma_status old_status = sdmac->status; + struct sdma_desc *desc = sdmac->desc; + int error = 0, cnt = 0; + enum dma_status old_status = sdmac->status; /* * loop mode. Iterate over descriptors, re-setup them and * call callback function. */ - while (sdmac->desc) { - struct sdma_desc *desc = sdmac->desc; + while (desc) { bd = &desc->bd[desc->buf_tail]; if (bd->mode.status & BD_DONE) break; + cnt++; + if (bd->mode.status & BD_RROR) { bd->mode.status &= ~BD_RROR; sdmac->status = DMA_ERROR; @@ -822,6 +824,17 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac) if (error) sdmac->status = old_status; } + + /* In some situations it may happen that the sdma does not found any + * usable descriptor in the ring to put data into. The channel is + * stopped then. While there is no specific error condition we can + * check for, a necessary condition is that all available buffers for + * the current channel have been written to by the sdma script. In + * this case and after we have made the buffers available again, + * we restart the channel. + */ + if (cnt >= desc->num_bd) + sdma_enable_channel(sdmac->sdma, sdmac->channel); } static void mxc_sdma_handle_channel_normal(struct sdma_channel *data) -- 2.23.0