From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2BCDCC433FF for ; Thu, 8 Aug 2019 12:33:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 01E0C2189F for ; Thu, 8 Aug 2019 12:33:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565267586; bh=KMINRkuYBok2QumR2R4JgROUPh1CgGn+fh9C0MQuJiE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=lr6ra7iJlHHULwJsKx0ekRe5sNOCml0rJu0FINkZwhPqtjo84tN5MTI2U9omI3Akk 2YYWTor3/0Aeo2vQWSjrEU4CuthmwD5WkTY66OEsuza6ngqgpDBnBxihY/BoYw+/4j ioUD5CybHD0gcXWtVVbczB8BEO+EX2MfptAjmBXs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390083AbfHHMdF (ORCPT ); Thu, 8 Aug 2019 08:33:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:47080 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389923AbfHHMdF (ORCPT ); Thu, 8 Aug 2019 08:33:05 -0400 Received: from localhost (unknown [122.178.245.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 778AA21883; Thu, 8 Aug 2019 12:33:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565267584; bh=KMINRkuYBok2QumR2R4JgROUPh1CgGn+fh9C0MQuJiE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rRHR+XO248Pa0ZDXn56QqJWmT9Z/E/aSJJ7Hi4HzJvTCl2kb91e3emsYz6phOwGU8 UDvpi8rzBAx/NX6r7HDbIBq+yDdlaqDK3fxdcC8fWu20Tr6kgV5WSSFnrCEglGU7Tj jLjsCWLb4MmUXsT7LQEfxdO4j60jkFPsgcJcC5zY= Date: Thu, 8 Aug 2019 18:01:52 +0530 From: Vinod Koul To: Lukas Wunner Cc: Mark Brown , Stefan Wahren , linux-spi@vger.kernel.org, dmaengine@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, bcm-kernel-feedback-list@broadcom.com, Eric Anholt , Nuno Sa , Martin Sperl , Noralf Tronnes , Robert Jarzmik , Florian Kauer , Florian Fainelli , Ray Jui , Scott Branden Subject: Re: [PATCH 09/10] dmaengine: bcm2835: Avoid accessing memory when copying zeroes Message-ID: <20190808123152.GW12733@vkoul-mobl.Dlink> References: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.11.3 (2019-02-01) Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org On 03-08-19, 12:10, Lukas Wunner wrote: > The BCM2835 DMA controller is capable of synthesizing zeroes instead of > copying them from a source address. The feature is enabled by setting > the SRC_IGNORE bit in the Transfer Information field of a Control Block: > > "Do not perform source reads. > In addition, destination writes will zero all the write strobes. > This is used for fast cache fill operations." > https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf > > The feature is only available on 8 of the 16 channels. The others are > so-called "lite" channels with a limited feature set and performance. > > Enable the feature if a cyclic transaction copies from the zero page. > This reduces traffic on the memory bus. > > A forthcoming use case is the BCM2835 SPI driver, which will cyclically > copy from the zero page to the TX FIFO. The idea to use SRC_IGNORE was > taken from an ancient GitHub conversation between Martin and Noralf: > https://github.com/msperl/spi-bcm2835/issues/13#issuecomment-98180451 Acked-by: Vinod Koul > > Tested-by: Nuno Sá > Signed-off-by: Lukas Wunner > Cc: Martin Sperl > Cc: Noralf Trønnes > Cc: Florian Kauer > --- > drivers/dma/bcm2835-dma.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c > index 14358faf3bff..67100e4e1083 100644 > --- a/drivers/dma/bcm2835-dma.c > +++ b/drivers/dma/bcm2835-dma.c > @@ -42,11 +42,14 @@ > * @ddev: DMA device > * @base: base address of register map > * @dma_parms: DMA parameters (to convey 1 GByte max segment size to clients) > + * @zero_page: bus address of zero page (to detect transactions copying from > + * zero page and avoid accessing memory if so) > */ > struct bcm2835_dmadev { > struct dma_device ddev; > void __iomem *base; > struct device_dma_parameters dma_parms; > + dma_addr_t zero_page; > }; > > struct bcm2835_dma_cb { > @@ -693,6 +696,7 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic( > size_t period_len, enum dma_transfer_direction direction, > unsigned long flags) > { > + struct bcm2835_dmadev *od = to_bcm2835_dma_dev(chan->device); > struct bcm2835_chan *c = to_bcm2835_dma_chan(chan); > struct bcm2835_desc *d; > dma_addr_t src, dst; > @@ -743,6 +747,10 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic( > dst = c->cfg.dst_addr; > src = buf_addr; > info |= BCM2835_DMA_D_DREQ | BCM2835_DMA_S_INC; > + > + /* non-lite channels can write zeroes w/o accessing memory */ > + if (buf_addr == od->zero_page && !c->is_lite_channel) > + info |= BCM2835_DMA_S_IGNORE; > } > > /* calculate number of frames */ > @@ -845,6 +853,9 @@ static void bcm2835_dma_free(struct bcm2835_dmadev *od) > list_del(&c->vc.chan.device_node); > tasklet_kill(&c->vc.task); > } > + > + dma_unmap_page_attrs(od->ddev.dev, od->zero_page, PAGE_SIZE, > + DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC); > } > > static const struct of_device_id bcm2835_dma_of_match[] = { > @@ -927,6 +938,14 @@ static int bcm2835_dma_probe(struct platform_device *pdev) > > platform_set_drvdata(pdev, od); > > + od->zero_page = dma_map_page_attrs(od->ddev.dev, ZERO_PAGE(0), 0, > + PAGE_SIZE, DMA_TO_DEVICE, > + DMA_ATTR_SKIP_CPU_SYNC); > + if (dma_mapping_error(od->ddev.dev, od->zero_page)) { > + dev_err(&pdev->dev, "Failed to map zero page\n"); > + return -ENOMEM; > + } > + > /* Request DMA channel mask from device tree */ > if (of_property_read_u32(pdev->dev.of_node, > "brcm,dma-channel-mask", > -- > 2.20.1 -- ~Vinod