From patchwork Fri Dec 11 15:58:40 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Daniel Vetter X-Patchwork-Id: 11968695 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=-18.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 36CF9C4361B for ; Fri, 11 Dec 2020 17:10:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0026A23DC2 for ; Fri, 11 Dec 2020 17:10:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406667AbgLKQAV (ORCPT ); Fri, 11 Dec 2020 11:00:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58560 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2406341AbgLKP7i (ORCPT ); Fri, 11 Dec 2020 10:59:38 -0500 Received: from mail-wm1-x343.google.com (mail-wm1-x343.google.com [IPv6:2a00:1450:4864:20::343]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 83BB8C0613CF for ; Fri, 11 Dec 2020 07:58:50 -0800 (PST) Received: by mail-wm1-x343.google.com with SMTP id y23so9073704wmi.1 for ; Fri, 11 Dec 2020 07:58:50 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=MaHCZAdgD/UD/VQUsOk2P9+31rgrVdxvdPUjva6U0D0=; b=dBiIfNYv+sMwwUJpozHRM5Ij3tA0ayCxirzqnF22PWNj+NAgWx2+A30gj3+An9jk8l K62Ha4GLOamQH54m1DNhnJr9j9kadnh/Vhy0XC4OsT49MhrZo68UfgdDrXb239AjwCuy NNm7q83o+jzUmSfkAxRiZuuBXUlVBT3HX5R5w= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=MaHCZAdgD/UD/VQUsOk2P9+31rgrVdxvdPUjva6U0D0=; b=lcCzNcX79wjQgGFvsi0MILnGAjU0y1ZO+gs1bsA2fU3bAhhHX57orzxrGz/k8uzz5f 1UhoBNH4rOA6tovgn/xX03B2WhNFyJ4vc8YfUGbJfeNXnPhlllx92habjNCUvuj4tNMx nuggr6KyP7m18wq8nAwhhHAyMrkwlps3wdXcFFC/uJRYBUWcgKggHu/5BYCwsCVuFOSd s/1XRG2cebnxuRep52NRN4m/A4Y+UGERszHtd8Kw0bvT4+pPVjeEH+wvpnbJZUyDk1pt sO/tKTp6ue7M/tii4hR8HeAMkou/BECiHjazYexFDiLfK0gy/oPdAY9nOMXzf/7nEQGM jWyg== X-Gm-Message-State: AOAM532JHljw/CnNkGH5Cb2dYf6SjQIIFNHAVkq9hphsIgGflbi32EB4 ryjYarXYW/F6bWxwj9cS5EhNEHgwstBQxw== X-Google-Smtp-Source: ABdhPJzp6riLVmKPkMw3+mlDUkh18/Y4i0QR8rA3Sfj5Yv5uXpu0DO9HIJGbDkZWtipf8LC0u1OFZw== X-Received: by 2002:a7b:c091:: with SMTP id r17mr10687617wmh.129.1607702329299; Fri, 11 Dec 2020 07:58:49 -0800 (PST) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id z21sm14828241wmk.20.2020.12.11.07.58.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Dec 2020 07:58:48 -0800 (PST) From: Daniel Vetter To: DRI Development Cc: Intel Graphics Development , Daniel Vetter , Daniel Vetter , Thomas Zimmermann , Sumit Semwal , =?utf-8?q?Christian_K=C3=B6nig?= , linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org Subject: [PATCH 1/4] dma-buf: Remove kmap kerneldoc vestiges Date: Fri, 11 Dec 2020 16:58:40 +0100 Message-Id: <20201211155843.3348718-1-daniel.vetter@ffwll.ch> X-Mailer: git-send-email 2.29.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Also try to clarify a bit when dma_buf_begin/end_cpu_access should be called. Signed-off-by: Daniel Vetter Cc: Thomas Zimmermann Cc: Sumit Semwal Cc: "Christian König" Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org --- drivers/dma-buf/dma-buf.c | 20 ++++++++++++++------ include/linux/dma-buf.h | 25 +++++++++---------------- 2 files changed, 23 insertions(+), 22 deletions(-) diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index e63684d4cd90..a12fdffa130f 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -1001,15 +1001,15 @@ EXPORT_SYMBOL_GPL(dma_buf_move_notify); * vmalloc space might be limited and result in vmap calls failing. * * Interfaces:: + * * void \*dma_buf_vmap(struct dma_buf \*dmabuf) * void dma_buf_vunmap(struct dma_buf \*dmabuf, void \*vaddr) * * The vmap call can fail if there is no vmap support in the exporter, or if - * it runs out of vmalloc space. Fallback to kmap should be implemented. Note - * that the dma-buf layer keeps a reference count for all vmap access and - * calls down into the exporter's vmap function only when no vmapping exists, - * and only unmaps it once. Protection against concurrent vmap/vunmap calls is - * provided by taking the dma_buf->lock mutex. + * it runs out of vmalloc space. Note that the dma-buf layer keeps a reference + * count for all vmap access and calls down into the exporter's vmap function + * only when no vmapping exists, and only unmaps it once. Protection against + * concurrent vmap/vunmap calls is provided by taking the &dma_buf.lock mutex. * * - For full compatibility on the importer side with existing userspace * interfaces, which might already support mmap'ing buffers. This is needed in @@ -1098,6 +1098,11 @@ static int __dma_buf_begin_cpu_access(struct dma_buf *dmabuf, * dma_buf_end_cpu_access(). Only when cpu access is braketed by both calls is * it guaranteed to be coherent with other DMA access. * + * This function will also wait for any DMA transactions tracked through + * implicit synchronization in &dma_buf.resv. For DMA transactions with explicit + * synchronization this function will only ensure cache coherency, callers must + * ensure synchronization with such DMA transactions on their own. + * * Can return negative error values, returns 0 on success. */ int dma_buf_begin_cpu_access(struct dma_buf *dmabuf, @@ -1199,7 +1204,10 @@ EXPORT_SYMBOL_GPL(dma_buf_mmap); * This call may fail due to lack of virtual mapping address space. * These calls are optional in drivers. The intended use for them * is for mapping objects linear in kernel space for high use objects. - * Please attempt to use kmap/kunmap before thinking about these interfaces. + * + * To ensure coherency users must call dma_buf_begin_cpu_access() and + * dma_buf_end_cpu_access() around any cpu access performed through this + * mapping. * * Returns 0 on success, or a negative errno code otherwise. */ diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index cf72699cb2bc..7eca37c8b10c 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -183,24 +183,19 @@ struct dma_buf_ops { * @begin_cpu_access: * * This is called from dma_buf_begin_cpu_access() and allows the - * exporter to ensure that the memory is actually available for cpu - * access - the exporter might need to allocate or swap-in and pin the - * backing storage. The exporter also needs to ensure that cpu access is - * coherent for the access direction. The direction can be used by the - * exporter to optimize the cache flushing, i.e. access with a different + * exporter to ensure that the memory is actually coherent for cpu + * access. The exporter also needs to ensure that cpu access is coherent + * for the access direction. The direction can be used by the exporter + * to optimize the cache flushing, i.e. access with a different * direction (read instead of write) might return stale or even bogus * data (e.g. when the exporter needs to copy the data to temporary * storage). * - * This callback is optional. + * Note that this is both called through the DMA_BUF_IOCTL_SYNC IOCTL + * command for userspace mappings established through @mmap, and also + * for kernel mappings established with @vmap. * - * FIXME: This is both called through the DMA_BUF_IOCTL_SYNC command - * from userspace (where storage shouldn't be pinned to avoid handing - * de-factor mlock rights to userspace) and for the kernel-internal - * users of the various kmap interfaces, where the backing storage must - * be pinned to guarantee that the atomic kmap calls can succeed. Since - * there's no in-kernel users of the kmap interfaces yet this isn't a - * real problem. + * This callback is optional. * * Returns: * @@ -216,9 +211,7 @@ struct dma_buf_ops { * * This is called from dma_buf_end_cpu_access() when the importer is * done accessing the CPU. The exporter can use this to flush caches and - * unpin any resources pinned in @begin_cpu_access. - * The result of any dma_buf kmap calls after end_cpu_access is - * undefined. + * undo anything else done in @begin_cpu_access. * * This callback is optional. *