Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752146AbbEAVHk (ORCPT ); Fri, 1 May 2015 17:07:40 -0400 Received: from 212-186-180-163.dynamic.surfer.at ([212.186.180.163]:48287 "EHLO cgate.sperl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751201AbbEAVHh convert rfc822-to-8bit (ORCPT ); Fri, 1 May 2015 17:07:37 -0400 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2098\)) Subject: Re: [PATCH v2] dmaengine: bcm2835: Add slave dma support From: Martin Sperl In-Reply-To: <1429355160-13657-1-git-send-email-noralf@tronnes.org> Date: Fri, 1 May 2015 23:07:33 +0200 Cc: dmaengine@vger.kernel.org, vinod.koul@intel.com, Linux Kernel Mailing List , jonathan@raspberrypi.org, linux-rpi-kernel , dan.j.williams@intel.com, linux-spi Content-Transfer-Encoding: 8BIT Message-Id: References: <1429355160-13657-1-git-send-email-noralf@tronnes.org> To: =?utf-8?Q?Noralf_Tr=C3=B8nnes?= , Stephen Warren X-Mailer: Apple Mail (2.2098) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1814 Lines: 47 Tests with the initial (and incomplete) version of the spi-bcm2835 driver with DMA transfer support show that the dma-engine works as expected with this patch. There is one one observation: > On 18.04.2015, at 13:06, Noralf Trønnes wrote: > +static struct dma_async_tx_descriptor * > +bcm2835_dma_prep_slave_sg(struct dma_chan *chan, > + struct scatterlist *sgl, > + unsigned int sg_len, > + enum dma_transfer_direction direction, > + unsigned long flags, void *context) > +{ ... > + /* Enable */ > + if (i == sg_len - 1 && len - j <= max_size) > + control_block->info |= BCM2835_DMA_INT_EN; The observation is that an interrupt is always triggered - even in the case where flags does NOT have DMA_PREP_INTERRUPT set. This may not be necessary and avoid interrupts. So maybe the above if clause should get extended by: && (flags & DMA_PREP_INTERRUPT) to only trigger an interrupt when really requested. I am not sure if there are any side-effects because of this besides having the requirement on the client to run dmaengine_terminate_all() on that specific dma channel without interrupts when the transfer is finished. In the case of SPI we have TX feed the fifo - which finishes early - , but we only need to the interrupt when RX finishes reading the fifo, which indicates that the SPI-transfer is fully finished. So having an interrupt on TX is not necessary for the process. The same observations may also apply to bcm2835_dma_prep_dma_cyclic (which is outside of this patch provided by Noralf). Martin -- 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/