From patchwork Tue Feb 25 23:58:55 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jason Ekstrand X-Patchwork-Id: 11405037 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 536F8930 for ; Tue, 25 Feb 2020 23:59:14 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (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 30E1821D7E for ; Tue, 25 Feb 2020 23:59:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=jlekstrand-net.20150623.gappssmtp.com header.i=@jlekstrand-net.20150623.gappssmtp.com header.b="uh/33vTQ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 30E1821D7E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=jlekstrand.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 54FAA890C5; Tue, 25 Feb 2020 23:59:10 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from mail-pj1-x1044.google.com (mail-pj1-x1044.google.com [IPv6:2607:f8b0:4864:20::1044]) by gabe.freedesktop.org (Postfix) with ESMTPS id CEE5D890C5 for ; Tue, 25 Feb 2020 23:59:08 +0000 (UTC) Received: by mail-pj1-x1044.google.com with SMTP id ep11so453687pjb.2 for ; Tue, 25 Feb 2020 15:59:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=jlekstrand-net.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=AF4yId+y/TfljEnxGOV4fCMRwsfaIal7EqJaU81pYYw=; b=uh/33vTQP+CF+n38KTauF2k2uBHZqxp8SnnNcBSRoRZX/gQ3o0rdcAYdUzw4HPkWGR 39YqylYPPNc8n/zdAzMqETA+F2vLwSR/MIMkOFfx2M4Aucz5qFquRZJ2QMIyE+ZzNCXq mYV7d6JH3e23j+QqLFAD1PhCm8c1QHkz6PxBRfBxIs2JpbHw9NWeo14B3v+W5s51E/n/ ngD2N0zbmXYJTCiuiykcrb5/0Pc0B3rCcdcBpiAZwwxoOsKoLY7v68ZAfraqUmgUCT5N JWzvd84LRlIzYA1QNK2UyXZxXY4EmZh8c3UafeF7oUHItNOBO34cvDbj6JcXiUpypxkF bOUQ== 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=AF4yId+y/TfljEnxGOV4fCMRwsfaIal7EqJaU81pYYw=; b=PG9nFe8IwjKgZJKytR75Z4PZ8qBi0oZF8XZqvqUOPnUtnCVaACkm4iYBZ815EU0suC vS89Aws4zrI2f1oo0bvD86asU34anu8M/20t1PjpJPfS87x3TWA9zsIVlz9WoYmxXlQl LpZ+ZV0rnvkTl/zGpztWk6vEHAg4EsEyFZ8SYAomsBMh05SbGGEe3nqm+Brk03UFpgS1 iLBSvF0MXflJ859DPZcgu2pSexRhxN3QR6X66HjmNQFysgUbgxaLsIebBBwM2s5HQfF+ 4ttkVo1Csq3HpugnZ+ygpmHBjNmwX9Am4T6QZn4FR5YLy+WtWS5dWyB46J7RMoXN2Gsq fO8g== X-Gm-Message-State: APjAAAWcmlnzL4XMOJNohLmJlk3WCVxi1iQjqg9DoMHp91Wk0EDKLrCV cLNbypVP612xV3h09S9rmaJtmQ== X-Google-Smtp-Source: APXvYqyaHbelULqZTMmN5KRFJiybbwwtp/zlDU+4paYLXPdoByk2DmIr7ueSCRJEhZcykFH/Cj08IQ== X-Received: by 2002:a17:902:8b89:: with SMTP id ay9mr1002292plb.309.1582675148262; Tue, 25 Feb 2020 15:59:08 -0800 (PST) Received: from omlet.com ([2605:6000:1026:c273::594]) by smtp.gmail.com with ESMTPSA id b15sm213974pft.58.2020.02.25.15.59.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Feb 2020 15:59:07 -0800 (PST) From: Jason Ekstrand To: Subject: [PATCH] RFC: dma-buf: Add an API for importing and exporting sync files Date: Tue, 25 Feb 2020 17:58:55 -0600 Message-Id: <20200225235856.975366-1-jason@jlekstrand.net> X-Mailer: git-send-email 2.24.1 MIME-Version: 1.0 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Chenbo Feng , daniels@collabora.com, daniel.vetter@ffwll.ch, jajones@nvidia.com, linux-kernel@vger.kernel.org, Greg Hackmann , linaro-mm-sig@lists.linaro.org, hoegsberg@google.com, dri-devel@lists.freedesktop.org, Jason Ekstrand , airlied@redhat.com, jessehall@google.com, christian.koenig@amd.com, linux-media@vger.kernel.org Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Explicit synchronization is the future. At least, that seems to be what most userspace APIs are agreeing on at this point. However, most of our Linux APIs (both userspace and kernel UAPI) are currently built around implicit synchronization with dma-buf. While work is ongoing to change many of the userspace APIs and protocols to an explicit synchronization model, switching over piecemeal is difficult due to the number of potential components involved. On the kernel side, many drivers use dma-buf including GPU (3D/compute), display, v4l, and others. In userspace, we have X11, several Wayland compositors, 3D drivers, compute drivers (OpenCL etc.), media encode/decode, and the list goes on. This patch provides a path forward by allowing userspace to manually manage the fences attached to a dma-buf. Alternatively, one can think of this as making dma-buf's implicit synchronization simply a carrier for an explicit fence. This is accomplished by adding two IOCTLs to dma-buf for importing and exporting a sync file to/from the dma-buf. This way a userspace component which is uses explicit synchronization, such as a Vulkan driver, can manually set the write fence on a buffer before handing it off to an implicitly synchronized component such as a Wayland compositor or video encoder. In this way, each of the different components can be upgraded to an explicit synchronization model one at a time as long as the userspace pieces connecting them are aware of it and import/export fences at the right times. There is a potential race condition with this API if userspace is not careful. A typical use case for implicit synchronization is to wait for the dma-buf to be ready, use it, and then signal it for some other component. Because a sync_file cannot be created until it is guaranteed to complete in finite time, userspace can only signal the dma-buf after it has already submitted the work which uses it to the kernel and has received a sync_file back. There is no way to atomically submit a wait-use-signal operation. This is not, however, really a problem with this API so much as it is a problem with explicit synchronization itself. The way this is typically handled is to have very explicit ownership transfer points in the API or protocol which ensure that only one component is using it at any given time. Both X11 (via the PRESENT extension) and Wayland provide such ownership transfer points via explicit present and idle messages. The decision was intentionally made in this patch to make the import and export operations IOCTLs on the dma-buf itself rather than as a DRM IOCTL. This makes it the import/export operation universal across all components which use dma-buf including GPU, display, v4l, and others. It also means that a userspace component can do the import/export without access to the DRM fd which may be tricky to get in cases where the client communicates with DRM via a userspace API such as OpenGL or Vulkan. At a future date we may choose to add direct import/export APIs to components such as drm_syncobj to avoid allocating a file descriptor and going through two ioctls. However, that seems to be something of a micro-optimization as import/export operations are likely to happen at a rate of a few per frame of rendered or decoded video. Signed-off-by: Jason Ekstrand --- This is marked as an RFC because I intend it to start a discussion about how to solve a problem. The current patch compiles but that's it for now. I'll be writing IGT tests and Vulkan driver patches which exercise it over the next couple of days. In the mean time, feel free to tell me why you think this is a great and/or terrible idea. :-) --Jason drivers/dma-buf/dma-buf.c | 115 +++++++++++++++++++++++++++++++++++ include/uapi/linux/dma-buf.h | 13 +++- 2 files changed, 126 insertions(+), 2 deletions(-) diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index d4097856c86b..3845b87e209e 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -20,6 +20,7 @@ #include #include #include +#include #include #include #include @@ -348,6 +349,114 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf) return ret; } +static long dma_buf_wait_sync_file(struct dma_buf *dmabuf, + const void __user *user_data) +{ + struct dma_buf_sync_file arg; + struct dma_fence *fence; + + if (copy_from_user(&arg, user_data, sizeof(arg))) + return -EFAULT; + + if (arg.flags != 0 && arg.flags != DMA_BUF_SYNC_FILE_SYNC_WRITE) + return -EINVAL; + + fence = sync_file_get_fence(arg.fd); + if (!fence) + return -EINVAL; + + if (arg.flags & DMA_BUF_SYNC_FILE_SYNC_WRITE) { + dma_resv_add_excl_fence(dmabuf->resv, fence); + } else { + dma_resv_add_shared_fence(dmabuf->resv, fence); + } + + return 0; +} + +static long dma_buf_signal_sync_file(struct dma_buf *dmabuf, + void __user *user_data) +{ + struct dma_buf_sync_file arg; + struct dma_fence *fence = NULL; + struct sync_file *sync_file; + int fd, ret; + + if (copy_from_user(&arg, user_data, sizeof(arg))) + return -EFAULT; + + if (arg.flags != 0 && arg.flags != DMA_BUF_SYNC_FILE_SYNC_WRITE) + return -EINVAL; + + fd = get_unused_fd_flags(O_CLOEXEC); + if (fd < 0) + return fd; + + if (arg.flags & DMA_BUF_SYNC_FILE_SYNC_WRITE) { + /* We need to include both the exclusive fence and all of + * the shared fences in our fence. + */ + struct dma_fence **fences = NULL; + unsigned i, num_fences = 0; + + ret = dma_resv_get_fences_rcu(dmabuf->resv, NULL, + &num_fences, &fences); + if (ret) + goto err_put_fd; + + if (num_fences == 0) { + fence = dma_fence_get_stub(); + } else if (num_fences == 1) { + fence = fences[0]; + kfree(fences); + } else { + struct dma_fence_array *fence_arr; + + fence_arr = dma_fence_array_create(num_fences, fences, + dma_fence_context_alloc(1), + 1, false); + if (!fence_arr) { + for (i = 0; i < num_fences; i++) + dma_fence_put(fences[i]); + kfree(fences); + ret = -ENOMEM; + goto err_put_fd; + } + + /* The fence array now owns fences_arr and our + * references to each of the individual fences. We + * only own a reference to the one array fence. + */ + fence = &fence_arr->base; + } + } else { + fence = dma_resv_get_excl_rcu(dmabuf->resv); + if (!fence) + fence = dma_fence_get_stub(); + } + + sync_file = sync_file_create(fence); + + dma_fence_put(fence); + + if (!sync_file) { + ret = -EINVAL; + goto err_put_fd; + } + + fd_install(fd, sync_file->file); + + arg.fd = fd; + if (copy_to_user(user_data, &arg, sizeof(arg))) + return -EFAULT; + + return 0; + +err_put_fd: + put_unused_fd(fd); + return ret; +} + static long dma_buf_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { @@ -390,6 +499,12 @@ static long dma_buf_ioctl(struct file *file, case DMA_BUF_SET_NAME: return dma_buf_set_name(dmabuf, (const char __user *)arg); + case DMA_BUF_IOCTL_WAIT_SYNC_FILE: + return dma_buf_wait_sync_file(dmabuf, (const void __user *)arg); + + case DMA_BUF_IOCTL_SIGNAL_SYNC_FILE: + return dma_buf_signal_sync_file(dmabuf, (void __user *)arg); + default: return -ENOTTY; } diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h index dbc7092e04b5..825b9a913c89 100644 --- a/include/uapi/linux/dma-buf.h +++ b/include/uapi/linux/dma-buf.h @@ -37,8 +37,17 @@ struct dma_buf_sync { #define DMA_BUF_NAME_LEN 32 +struct dma_buf_sync_file { + __u32 flags; + __s32 fd; +}; + +#define DMA_BUF_SYNC_FILE_SYNC_WRITE (1 << 0) + #define DMA_BUF_BASE 'b' -#define DMA_BUF_IOCTL_SYNC _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync) -#define DMA_BUF_SET_NAME _IOW(DMA_BUF_BASE, 1, const char *) +#define DMA_BUF_IOCTL_SYNC _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync) +#define DMA_BUF_SET_NAME _IOW(DMA_BUF_BASE, 1, const char *) +#define DMA_BUF_IOCTL_WAIT_SYNC_FILE _IOW(DMA_BUF_BASE, 2, struct dma_buf_sync) +#define DMA_BUF_IOCTL_SIGNAL_SYNC_FILE _IOW(DMA_BUF_BASE, 3, struct dma_buf_sync) #endif