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bh=2S1GZjVV0O2eW26D/C5mP/xBfS/QZ8D4wdzglA9JkS8=; b=m6G4l+FIBEhqEn2P3pVAPi9Edtrz0lBR/DREKWmORwciEtiaVRFWXCxavfNB2vfqQHrq3f agIbKULr9+h1IkDg== Received: from director2.suse.de ([192.168.254.72]) by imap3-int with ESMTPSA id KiC9MnCp0WASIwAALh3uQQ (envelope-from ); Tue, 22 Jun 2021 09:12:16 +0000 Subject: Re: [PATH 0/4] [RFC] Support virtual DRM To: Esaki Tomohito Cc: devicetree@vger.kernel.org, Takanari Hayama , linux-doc@vger.kernel.org, David Airlie , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-renesas-soc@vger.kernel.org, Kieran Bingham , Laurent Pinchart , Damian Hobson-Garcia References: <20210621062742.26073-1-etom@igel.co.jp> <9853d0a9-6053-db64-9c79-40b7e0689eec@suse.de> <85593f2f-5aa9-6023-ecba-c5275a468b71@igel.co.jp> From: Thomas Zimmermann Message-ID: Date: Tue, 22 Jun 2021 11:12:16 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <85593f2f-5aa9-6023-ecba-c5275a468b71@igel.co.jp> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="WlcHhU6hex4h9Z0LOqBGwvBjeuF1z7K0S" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --WlcHhU6hex4h9Z0LOqBGwvBjeuF1z7K0S Content-Type: multipart/mixed; boundary="Kk1kL8IpnwdpIdgA1q2JbHjX2dsQ44t2z"; protected-headers="v1" From: Thomas Zimmermann To: Esaki Tomohito Cc: devicetree@vger.kernel.org, Takanari Hayama , linux-doc@vger.kernel.org, David Airlie , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-renesas-soc@vger.kernel.org, Kieran Bingham , Laurent Pinchart , Damian Hobson-Garcia Message-ID: Subject: Re: [PATH 0/4] [RFC] Support virtual DRM References: <20210621062742.26073-1-etom@igel.co.jp> <9853d0a9-6053-db64-9c79-40b7e0689eec@suse.de> <85593f2f-5aa9-6023-ecba-c5275a468b71@igel.co.jp> In-Reply-To: <85593f2f-5aa9-6023-ecba-c5275a468b71@igel.co.jp> --Kk1kL8IpnwdpIdgA1q2JbHjX2dsQ44t2z Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable Hi Am 22.06.21 um 06:02 schrieb Esaki Tomohito: > Hi, Thomas > Thank you for reply. >=20 > 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 solv= ed >> in userspace? >=20 > 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, th= e > image will be displayed at the next VSYNC, so it will be displayed afte= r > 1 VSYNC at most. Other commenters already addressed these points. >=20 > Also, since the compositor is a single point of failure, we may not wan= t > to make it dependent on it. The kernel is also a single point of failure. TBH I don't think this feature should be merged until there's a clear=20 use case that cannot be solved in userspace idiomatically. Best regards Thomas >=20 > Best regards > Tomohito Esaki >=20 --=20 Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 N=C3=BCrnberg, Germany (HRB 36809, AG N=C3=BCrnberg) Gesch=C3=A4ftsf=C3=BChrer: Felix Imend=C3=B6rffer --Kk1kL8IpnwdpIdgA1q2JbHjX2dsQ44t2z-- --WlcHhU6hex4h9Z0LOqBGwvBjeuF1z7K0S Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature" -----BEGIN PGP SIGNATURE----- wsF5BAABCAAjFiEExndm/fpuMUdwYFFolh/E3EQov+AFAmDRqXAFAwAAAAAACgkQlh/E3EQov+Af LhAAl2DsZ+2q/Kykruu+aUiljCoeGL+fehatgi3Qbz9LHotnb+8lcZL8qNGjphWQxLpooqeO9ZDr WPop9s6a4mSHD9nyyvXrdWLdid5wYpmetCMH6SVXHMlVWh+n/qw9v49DtqxHEADDk5VixNgh9cxQ RbRmOVg88YT8Z40zAZw2I6MlmIpS0SSDE5yjR3JHE6zOI6bniAdGiiCKojqoIS/Md/9g4MBjsIk2 lro7eW7ulINyEuoDnbY3M241s/cZnP/ZShARtgScL5bVhoQZ6s7YO8OISYhYdkg+eF1qi1AdsqZY pmDLtAhZ95arQa5OIVTGewxxCG/uzbIDUh4v4lJSgBSF0SUtakCJF9Q9AhjCvW1+era0253MfyCy /F5sndCQh/Iaqt6hpqe6ijC5RgA4Le7IUBBZV+HE48/9hRv6QqZSEVz61LvpbK2mFihJYxFPfTwS xxa1E/+HvWDuEgUeehAWqaL07ytWPoaQBqn9nSvAtXTNPbXiknOWqW7Vq3vUMmf/zpF6mkd8R89U um6D6/bEIu0Vd9ZK5blNbuzoX+g/qJpWU+As8jkXF1uR0tDHPq2OsokaWQ2IsDkoJT4DBzzgFcl9 RaTrRoKwCoEGIZfu1Bg4cfMPi6T0BmXiWs+psao3lp1Dwpiz8FMMRG6ObJ/0hcZ5g5B6+gugbqjb /Og= =+9bo -----END PGP SIGNATURE----- --WlcHhU6hex4h9Z0LOqBGwvBjeuF1z7K0S--