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([240b:10:c9a0:ca00:5192:32ad:e5be:23cd]) by smtp.gmail.com with ESMTPSA id x20sm16719962pfh.112.2021.06.21.21.03.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Jun 2021 21:03:03 -0700 (PDT) Subject: Re: [PATH 0/4] [RFC] Support virtual DRM To: Thomas Zimmermann Cc: Maarten Lankhorst , Maxime Ripard , David Airlie , Daniel Vetter , Laurent Pinchart , Kieran Bingham , dri-devel@lists.freedesktop.org, linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-doc@vger.kernel.org, Damian Hobson-Garcia , Takanari Hayama References: <20210621062742.26073-1-etom@igel.co.jp> <9853d0a9-6053-db64-9c79-40b7e0689eec@suse.de> From: Esaki Tomohito Message-ID: <85593f2f-5aa9-6023-ecba-c5275a468b71@igel.co.jp> Date: Tue, 22 Jun 2021 13:02:59 +0900 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <9853d0a9-6053-db64-9c79-40b7e0689eec@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Thomas Thank you for reply. On 2021/06/21 16:10, Thomas Zimmermann wrote: > Hi > > Am 21.06.21 um 08:27 schrieb Tomohito Esaki: >> Virtual DRM splits the overlay planes of a display controller into >> multiple >> virtual devices to allow each plane to be accessed by each process. >> >> This makes it possible to overlay images output from multiple >> processes on a >> display. For example, one process displays the camera image without >> compositor >> while another process overlays the UI. > > I briefly looked over your patches. I didn't understand how this is > different to the functionality of a compositor? Shouldn't this be solved > in userspace? I think when latency is important (e.g., AR, VR, for displaying camera images in IVI systems), there may be use cases where the compositor cannot be used. Normally, when the image is passed through the compositor, it is displayed after 2 VSYNC at most, because the compositor combines the image with VSYNC synchronization. On the other hand, if we use vDRM, the image will be displayed at the next VSYNC, so it will be displayed after 1 VSYNC at most. Also, since the compositor is a single point of failure, we may not want to make it dependent on it. Best regards Tomohito Esaki