From patchwork Mon Aug 12 14:22:11 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Jason Ekstrand X-Patchwork-Id: 11089929 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 28AE914DB for ; Mon, 12 Aug 2019 14:22:23 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 17CCB2832D for ; Mon, 12 Aug 2019 14:22:23 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 0C3D428113; Mon, 12 Aug 2019 14:22:23 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 3853E2832D for ; Mon, 12 Aug 2019 14:22:22 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 59E7E6E536; Mon, 12 Aug 2019 14:22:21 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from mail-pl1-x643.google.com (mail-pl1-x643.google.com [IPv6:2607:f8b0:4864:20::643]) by gabe.freedesktop.org (Postfix) with ESMTPS id 127F96E53E for ; Mon, 12 Aug 2019 14:22:20 +0000 (UTC) Received: by mail-pl1-x643.google.com with SMTP id z3so1110547pln.6 for ; Mon, 12 Aug 2019 07:22:20 -0700 (PDT) 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:in-reply-to :references:mime-version:content-transfer-encoding; bh=MTM2UrnDTQBhu67URTLpEXS3+O65wVwvDkNrdk4cqnw=; b=jt2aCEBQyn5+UnYZ6lFHBHKS+spnymVY3TAASA2qJJyIzYlKaFgeCac2+E0nnFEkGk dOzxRlOGHqfVxewQFxNuMuShvAaegfa9j7BkRd54OnfZhIdzp4v7aqQzMCzb6vqAO2rw 6Ww0rpmITQvFRBs+TP9DQj+KIdhj1dMtGALgnhX7mgCqDguMKggdVt2ctJXHjiEeQ6vk 74MArJQDd4iSCtBsbNfVMrtCOgqSr9qdb5WGMjiJn9TC3crXDYJTiyy6yEAtjVrzoFgs TSb81MNkMr/Q42RL20qHM+0P+MkL7ck143wkX0ZXtGKv9KZltzYNRLc8UdPSe/2IYwss O+7g== X-Gm-Message-State: APjAAAVvW+9fcNT/fW3nH4iq/YArzPdU9qRrb116/LBii4gb5H9u5Yet RsTtPQLK06UN2dX5OFiPZNInDCBFrBQ= X-Google-Smtp-Source: APXvYqw7c1+C+ZrQAIItdzyT9ws2iqBaAGONmsdrDjw3r9Gah810yLOFxuF6Ni2l4mZFb2xfzmPIaw== X-Received: by 2002:a17:902:a606:: with SMTP id u6mr1916157plq.224.1565619739024; Mon, 12 Aug 2019 07:22:19 -0700 (PDT) Received: from omlet.jf.intel.com ([2605:6000:1026:c030::a57]) by smtp.gmail.com with ESMTPSA id x9sm78734009pgp.75.2019.08.12.07.22.17 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 12 Aug 2019 07:22:18 -0700 (PDT) From: Jason Ekstrand To: dri-devel@lists.freedesktop.org Subject: [PATCH] drm/syncobj: Add better overview documentation for syncobj (v2) Date: Mon, 12 Aug 2019 09:22:11 -0500 Message-Id: <20190812142211.15885-1-jason@jlekstrand.net> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190806161905.30769-1-jason@jlekstrand.net> References: <20190806161905.30769-1-jason@jlekstrand.net> MIME-Version: 1.0 X-Mailman-Original-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:in-reply-to:references :mime-version:content-transfer-encoding; bh=MTM2UrnDTQBhu67URTLpEXS3+O65wVwvDkNrdk4cqnw=; b=qc8nnozD2qiGVdffjvGB2YmU0/bsVKP29Y/JvBLrpwqTT/hRH4UZ7tOLhvUKtHAEGH UKfeXG8fF1a7XWOpkbzwgsgRiojr8lM8p7M9nswdcX1zitYGzp0r9Se9LGiu7iquAEEk AOWg1qYVNBsUUiMHd8NoF+xwlZX3aflmDlL/sU2+TX4XqQCcTtTRdWIxsWr1MMFiIz6r Tpk+zkLhFXYDt6f6ng7XGXlzFerLn2+Uk8PNOO652zX2x4tcrQBrXJUGW5Ne25cMoCAT wFxV2qAokM6BVxbfsQ/zq9MqRunLjZS39R/LbWnJ5IsnrjKKNQqAuuTADHVZTyEd2FuL Cd9A== X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jason Ekstrand , =?utf-8?q?Christian_K=C3=B6nig?= Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" X-Virus-Scanned: ClamAV using ClamSMTP This patch only brings the syncobj documentation up-to-date for the original form of syncobj. It does not contain any information about the design of timeline syncobjs. v2: Incorporate feedback from Lionel and Christian: - Mention actual ioctl and flag names - Better language around reference counting - Misc. language cleanups Signed-off-by: Jason Ekstrand Reviewed-by: Lionel Landwerlin Acked-by: Christian König --- drivers/gpu/drm/drm_syncobj.c | 98 +++++++++++++++++++++++++++++++---- 1 file changed, 87 insertions(+), 11 deletions(-) diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c index 1438dcb3ebb1..4b5c7b0ed714 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/drivers/gpu/drm/drm_syncobj.c @@ -29,21 +29,97 @@ /** * DOC: Overview * - * DRM synchronisation objects (syncobj, see struct &drm_syncobj) are - * persistent objects that contain an optional fence. The fence can be updated - * with a new fence, or be NULL. + * DRM synchronisation objects (syncobj, see struct &drm_syncobj) provide a + * container for a synchronization primitive which can be used by userspace + * to explicitly synchronize GPU commands, can be shared between userspace + * processes, and can be shared between different DRM drivers. + * Their primary use-case is to implement Vulkan fences and semaphores. + * The syncobj userspace API provides ioctls for several operations: * - * syncobj's can be waited upon, where it will wait for the underlying - * fence. + * - Creation and destruction of syncobjs + * - Import and export of syncobjs to/from a syncobj file descriptor + * - Import and export a syncobj's underlying fence to/from a sync file + * - Reset a syncobj (set its fence to NULL) + * - Signal a syncobj (set a trivially signaled fence) + * - Wait for a syncobj's fence to appear and be signaled * - * syncobj's can be export to fd's and back, these fd's are opaque and - * have no other use case, except passing the syncobj between processes. + * At it's core, a syncobj is simply a wrapper around a pointer to a struct + * &dma_fence which may be NULL. + * When a syncobj is first created, its pointer is either NULL or a pointer + * to an already signaled fence depending on whether the + * &DRM_SYNCOBJ_CREATE_SIGNALED flag is passed to + * &DRM_IOCTL_SYNCOBJ_CREATE. + * When GPU work which signals a syncobj is enqueued in a DRM driver, + * the syncobj fence is replaced with a fence which will be signaled by the + * completion of that work. + * When GPU work which waits on a syncobj is enqueued in a DRM driver, the + * driver retrieves syncobj's current fence at the time the work is enqueued + * waits on that fence before submitting the work to hardware. + * If the syncobj's fence is NULL, the enqueue operation is expected to fail. + * All manipulation of the syncobjs's fence happens in terms of the current + * fence at the time the ioctl is called by userspace regardless of whether + * that operation is an immediate host-side operation (signal or reset) or + * or an operation which is enqueued in some driver queue. + * &DRM_IOCTL_SYNCOBJ_RESET and &DRM_IOCTL_SYNCOBJ_SIGNAL can be used to + * manipulate a syncobj from the host by resetting its pointer to NULL or + * setting its pointer to a fence which is already signaled. * - * Their primary use-case is to implement Vulkan fences and semaphores. * - * syncobj have a kref reference count, but also have an optional file. - * The file is only created once the syncobj is exported. - * The file takes a reference on the kref. + * Host-side wait on syncobjs + * -------------------------- + * + * &DRM_IOCTL_SYNCOBJ_WAIT takes an array of syncobj handles and does a + * host-side wait on all of the syncobj fences simultaneously. + * If &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL is set, the wait ioctl will wait on + * all of the syncobj fences to be signaled before it returns. + * Otherwise, it returns once at least one syncobj fence has been signaled + * and the index of a signaled fence is written back to the client. + * + * Unlike the enqueued GPU work dependencies which fail if they see a NULL + * fence in a syncobj, if &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT is set, + * the host-side wait will first wait for the syncobj to receive a non-NULL + * fence and then wait on that fence. + * If &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT is not set and any one of the + * syncobjs in the array has a NULL fence, -EINVAL will be returned. + * Assuming the syncobj starts off with a NULL fence, this allows a client + * to do a host wait in one thread (or process) which waits on GPU work + * submitted in another thread (or process) without having to manually + * synchronize between the two. + * This requirement is inherited from the Vulkan fence API. + * + * + * Import/export of syncobjs + * ------------------------- + * + * &DRM_IOCTL_SYNCOBJ_FD_TO_HANDLE and &DRM_IOCTL_SYNCOBJ_HANDLE_TO_FD + * provide two mechanisms for import/export of syncobjs. + * + * The first lets the client import or export an entire syncobj to a file + * descriptor. + * These fd's are opaque and have no other use case, except passing the + * syncobj between processes. + * All exported file descriptors and any syncobj handles created as a + * result of importing those file descriptors own a reference to the + * same underlying struct &drm_syncobj and the syncobj can be used + * persistently across all the processes with which it is shared. + * The syncobj is freed only once the last reference is dropped. + * Unlike dma-buf, importing a syncobj creates a new handle (with its own + * reference) for every import instead of de-duplicating. + * The primary use-case of this persistent import/export is for shared + * Vulkan fences and semaphores. + * + * The second import/export mechanism, which is indicated by + * &DRM_SYNCOBJ_FD_TO_HANDLE_FLAGS_IMPORT_SYNC_FILE or + * &DRM_SYNCOBJ_HANDLE_TO_FD_FLAGS_EXPORT_SYNC_FILE lets the client + * import/export the syncobj's current fence from/to a &sync_file. + * When a syncobj is exported to a sync file, that sync file wraps the + * sycnobj's fence at the time of export and any later signal or reset + * operations on the syncobj will not affect the exported sync file. + * When a sync file is imported into a syncobj, the syncobj's fence is set + * to the fence wrapped by that sync file. + * Because sync files are immutable, resetting or signaling the syncobj + * will not affect any sync files whose fences have been imported into the + * syncobj. */ #include