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We need to exchange some sort of metadata between drivers, likes dynamic HDR data between video4linux2 and DRM. Or the graphics frame buffer is too complex to be described with plain plane's DMA-buf fd. An issue between DRM and V4L2 is that DRM could only support 4 planes while it is 8 for V4L2. It would be pretty hard for DRM to expend its interface to support that 4 more planes which would lead to revision of many standard likes Vulkan, EGL. Also, there is no reason to consume a device's memory for the content that device can't read it, or wasting an entry of IOMMU for such data. Usually, such a metadata would be the value should be written to a hardware's registers, a 4KiB page would be 1024 items of 32 bits registers. Still, I have some problems with SHMEM: 1. I don't want thhe userspace modify the context of the SHMEM allocated by the kernel, is there a way to do so? 2. Should I create a helper function for installing the SHMEM file as a fd? -- Hsia-Jun(Randy) Li 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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2B550EE4993 for ; Tue, 22 Aug 2023 11:14:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234610AbjHVLOw (ORCPT ); Tue, 22 Aug 2023 07:14:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38800 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233729AbjHVLOv (ORCPT ); Tue, 22 Aug 2023 07:14:51 -0400 Received: from NAM04-DM6-obe.outbound.protection.outlook.com (mail-dm6nam04on2054.outbound.protection.outlook.com [40.107.102.54]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C1940CD1; Tue, 22 Aug 2023 04:14:49 -0700 (PDT) ARC-Seal: i=1; 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Tue, 22 Aug 2023 11:14:45 +0000 Message-ID: <029b982f-da62-4fa8-66c4-ab11a515574a@synaptics.com> Date: Tue, 22 Aug 2023 19:14:35 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 From: Hsia-Jun Li Content-Language: en-GB To: linux-mm@kvack.org Cc: dri-devel@lists.freedesktop.org, Linux Media Mailing List , hughd@google.com, akpm@linux-foundation.org, Simon Ser , Hans Verkuil , Tomasz Figa , daniels@collabora.com, ayaka , linux-kernel@vger.kernel.org Subject: [RFC]: shmem fd for non-DMA buffer sharing cross drivers Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: PH8PR07CA0021.namprd07.prod.outlook.com (2603:10b6:510:2cd::10) To DM6PR03MB5196.namprd03.prod.outlook.com (2603:10b6:5:24a::19) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR03MB5196:EE_|MN2PR03MB5118:EE_ X-MS-Office365-Filtering-Correlation-Id: a54fec06-acce-4dc2-6fb5-08dba300fd83 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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We need to exchange some sort of metadata between drivers, likes dynamic HDR data between video4linux2 and DRM. Or the graphics frame buffer is too complex to be described with plain plane's DMA-buf fd. An issue between DRM and V4L2 is that DRM could only support 4 planes while it is 8 for V4L2. It would be pretty hard for DRM to expend its interface to support that 4 more planes which would lead to revision of many standard likes Vulkan, EGL. Also, there is no reason to consume a device's memory for the content that device can't read it, or wasting an entry of IOMMU for such data. Usually, such a metadata would be the value should be written to a hardware's registers, a 4KiB page would be 1024 items of 32 bits registers. Still, I have some problems with SHMEM: 1. I don't want thhe userspace modify the context of the SHMEM allocated by the kernel, is there a way to do so? 2. Should I create a helper function for installing the SHMEM file as a fd? -- Hsia-Jun(Randy) Li