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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_GIT 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 355A6C6778D for ; Tue, 11 Sep 2018 16:31:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D13CE2086E for ; Tue, 11 Sep 2018 16:31:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D13CE2086E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=sang-engineering.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727998AbeIKVbR (ORCPT ); Tue, 11 Sep 2018 17:31:17 -0400 Received: from sauhun.de ([88.99.104.3]:53630 "EHLO pokefinder.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726775AbeIKVbR (ORCPT ); Tue, 11 Sep 2018 17:31:17 -0400 Received: from localhost (i577B9DAC.versanet.de [87.123.157.172]) by pokefinder.org (Postfix) with ESMTPSA id E38BF2CF608; Tue, 11 Sep 2018 18:31:09 +0200 (CEST) From: Wolfram Sang To: iommu@lists.linux-foundation.org, Robin Murphy Cc: linux-renesas-soc@vger.kernel.org, Christoph Hellwig , Marek Szyprowski , linux-kernel@vger.kernel.org, Wolfram Sang Subject: [RFC PATCH 0/2] dma-mapping: introduce helper for setting dma_parms Date: Tue, 11 Sep 2018 18:30:48 +0200 Message-Id: <20180911163050.28072-1-wsa+renesas@sang-engineering.com> X-Mailer: git-send-email 2.18.0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, commit 78c47830a5cb ("dma-debug: check scatterlist segments") triggers for Renesas hardware I look after, so thanks for pointing out we should have proper dma_parms for our DMA providers. When trying to fix it, I became a bit puzzled about the life cycle of the pointer to dma_parms. AFAIU most drivers leave the pointer dangling on driver unbind. Check drivers/dma/bcm2835-dma.c, for example: od = devm_kzalloc(&pdev->dev, sizeof(*od), GFP_KERNEL); if (!od) return -ENOMEM; pdev->dev.dma_parms = &od->dma_parms; dma_set_max_seg_size(&pdev->dev, 0x3FFFFFFF); And that's all about handling dma_parms. So, on unbind, the memory for 'od' gets freed and dma_params is a dangling pointer. drivers/gpu/drm/exynos/exynos_drm_iommu.c seems to do it correctly: static inline int configure_dma_max_seg_size(struct device *dev) { if (!dev->dma_parms) dev->dma_parms = kzalloc(sizeof(*dev->dma_parms), GFP_KERNEL); if (!dev->dma_parms) return -ENOMEM; dma_set_max_seg_size(dev, DMA_BIT_MASK(32)); return 0; } static inline void clear_dma_max_seg_size(struct device *dev) { kfree(dev->dma_parms); dev->dma_parms = NULL; } But this seems error prone and quite some code to add for every DMA provider. So, I wondered if we couldn't have a helper for that. After some brainstorming, I favour a dmam_-type of function. It will ensure the memory gets freed and the pointer cleared on unbind. And it should be easy to use. I attached an RFC which I tested on a Renesas R-Car H3 SoC with the internal DMAC of the SD controller. A branch can be found here (still waiting for buildbot results): git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git renesas/sdhi/set_max_seg I added the companion function dmam_free_dma_parms() for completeness although there is no user yet. I'd be totally open to drop it until someone needs it. Please let me know what you think. If this is the right track, I'll be willing to fix the dangling pointers with it, too. Thanks and happy hacking, Wolfram Wolfram Sang (2): dma-mapping: introduce helper for setting dma_parms mmc: sdhi: internal_dmac: set dma_parms drivers/mmc/host/renesas_sdhi_internal_dmac.c | 2 + include/linux/dma-mapping.h | 5 ++ kernel/dma/mapping.c | 50 +++++++++++++++++++ 3 files changed, 57 insertions(+) -- 2.18.0