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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, 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 BC2C3C433E0 for ; Wed, 27 Jan 2021 15:56:19 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E4679207D0 for ; Wed, 27 Jan 2021 15:56:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E4679207D0 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 67376869AA; Wed, 27 Jan 2021 15:56:18 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 9-ticpTfdX7Q; Wed, 27 Jan 2021 15:56:17 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by whitealder.osuosl.org (Postfix) with ESMTP id B1AB6869A7; Wed, 27 Jan 2021 15:56:17 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 6AD29C08A1; Wed, 27 Jan 2021 15:56:17 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) by lists.linuxfoundation.org (Postfix) with ESMTP id E815DC013A for ; Wed, 27 Jan 2021 15:56:15 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id CED5986132 for ; Wed, 27 Jan 2021 15:56:15 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ft7acrPuClwO for ; Wed, 27 Jan 2021 15:56:13 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by hemlock.osuosl.org (Postfix) with ESMTPS id 9357686113 for ; Wed, 27 Jan 2021 15:56:13 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 5554C68AFE; Wed, 27 Jan 2021 16:56:08 +0100 (CET) Date: Wed, 27 Jan 2021 16:56:08 +0100 From: ". Christoph Hellwig" To: Ricardo Ribalda Subject: Re: [PATCH v3 5/6] media: uvcvideo: Use dma_alloc_noncontiguos API Message-ID: <20210127155608.GA20272@lst.de> References: <20201201033658.GE3723071@google.com> <20201201144916.GA14682@lst.de> <20201208071320.GA1667627@google.com> <20201209111639.GB22806@lst.de> <20210111083614.GA27589@lst.de> <20210126170659.GA9104@lst.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Cc: Sergey Senozhatsky , Sergey Senozhatsky , Linux Doc Mailing List , Linux Kernel Mailing List , IOMMU DRIVERS , Linux Media Mailing List , Mauro Carvalho Chehab , Robin Murphy , ". Christoph Hellwig" X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Wed, Jan 27, 2021 at 12:29:08AM +0100, Ricardo Ribalda wrote: > - Is there any platform where dma_alloc_noncontiguos can fail? > This is, !ops->alloc_noncontiguous and !dev->coherent_dma_mask > If yes then we need to add a function to let the driver know in > advance that it has to use the coherent allocator (usb_alloc_coherent > for uvc) dev->coherent_dma_mask is set by the driver. So the only reason why dma_alloc_noncontiguos will fail is because is because it can't allocate any memory. > - In dma_alloc_noncontiguos, on the dma_alloc_pages fallback. If we > have a device where the dma happens in only one direction, could not > get more performance with DMA_FROM/TO_DEVICE instead of > DMA_BIDIRECTIONAL ? Yes, we could probably do that. > > > Then I have tried to use the API, and I have encountered a problem: on > uvcvideo the device passed to the memory allocator is different for > DMA_PAGES and NON_CONTIGUOUS: > https://github.com/ribalda/linux/blob/042cd497739f71c8d4a83a67ee970369e2baca4a/drivers/media/usb/uvc/uvc_video.c#L1236 > > I need to dig a bit tomorrow to figure out why this is, I have > hardware to test both paths, so it should not be too difficult. I always found the USB dma alloc API a little weird, but we might have to follow the scheme of the usb coherent wrappers there. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu