From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.bootlin.com ([62.4.15.54]:45787 "EHLO mail.bootlin.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726468AbeHFLVV (ORCPT ); Mon, 6 Aug 2018 07:21:21 -0400 Message-ID: Subject: Re: [RFC] Request API and V4L2 capabilities From: Paul Kocialkowski To: Hans Verkuil , Linux Media Mailing List , Sakari Ailus , Laurent Pinchart , Tomasz Figa , Maxime Ripard , Mauro Carvalho Chehab Date: Mon, 06 Aug 2018 11:13:12 +0200 In-Reply-To: <5f1a88aa-9ad9-9669-b8b9-78c921282279@xs4all.nl> References: <621896b1-f26e-3239-e7e7-e8c9bc4f3fe8@xs4all.nl> <43c3d4b79377e9481ca29308cf1c160d57902d8c.camel@bootlin.com> <5f1a88aa-9ad9-9669-b8b9-78c921282279@xs4all.nl> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-+VTkoTexxFsbtNEWLvNM" Mime-Version: 1.0 Sender: linux-media-owner@vger.kernel.org List-ID: --=-+VTkoTexxFsbtNEWLvNM Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi, On Mon, 2018-08-06 at 10:32 +0200, Hans Verkuil wrote: > On 08/06/2018 10:16 AM, Paul Kocialkowski wrote: > > On Sat, 2018-08-04 at 15:50 +0200, Hans Verkuil wrote: > > > Regarding point 3: I think this should be documented next to the pixe= l format. I.e. > > > the MPEG-2 Slice format used by the stateless cedrus codec requires t= he request API > > > and that two MPEG-2 controls (slice params and quantization matrices)= must be present > > > in each request. > > >=20 > > > I am not sure a control flag (e.g. V4L2_CTRL_FLAG_REQUIRED_IN_REQ) is= needed here. > > > It's really implied by the fact that you use a stateless codec. It do= esn't help > > > generic applications like v4l2-ctl or qv4l2 either since in order to = support > > > stateless codecs they will have to know about the details of these co= ntrols anyway. > > >=20 > > > So I am inclined to say that it is not necessary to expose this infor= mation in > > > the API, but it has to be documented together with the pixel format d= ocumentation. > >=20 > > I think this is affected by considerations about codec profile/level > > support. More specifically, some controls will only be required for > > supporting advanced codec profiles/levels, so they can only be > > explicitly marked with appropriate flags by the driver when the target > > profile/level is known. And I don't think it would be sane for userspac= e > > to explicitly set what profile/level it's aiming at. As a result, I > > don't think we can explicitly mark controls as required or optional. > >=20 > > I also like the idea that it should instead be implicit and that the > > documentation should detail which specific stateless metadata controls > > are required for a given profile/level. > >=20 > > As for controls validation, the approach followed in the Cedrus driver > > is to check that the most basic controls are filled and allow having > > missing controls for those that match advanced profiles. > >=20 > > Since this approach feels somewhat generic enough to be applied to all > > stateless VPU drivers, maybe this should be made a helper in the > > framework? >=20 > Sounds reasonable. Not sure if it will be in the first version, but it is > easy to add later. Definitely, I don't think this is such a high priority for now either. > > In addition, I see a need for exposing the maximum profile/level that > > the driver supports for decoding. I would suggest reusing the already- > > existing dedicated controls used for encoding for this purpose. For > > decoders, they would be used to expose the (read-only) maximum > > profile/level that is supported by the hardware and keep using them as = a > > settable value in a range (matching the level of support) for encoders. > >=20 > > This is necessary for userspace to determine whether a given video can > > be decoded in hardware or not. Instead of half-way decoding the video > > (ending up in funky results), this would easily allow skipping hardware > > decoding and e.g. falling back on software decoding. >=20 > I think it might be better to expose this through new read-only bitmask > controls: i.e. a bitmask containing the supported profiles and levels. It seems that this is more or less what the coda driver is doing for decoding actually, although it uses a menu control between min/max supported profile/levels, with a mask to "blacklist" the unsupported values. Then, the V4L2_CTRL_FLAG_READ_ONLY flag is set to keep the control read-only. > Reusing the existing controls for a decoder is odd since there is not > really a concept of a 'current' value since you just want to report what > is supported. And I am not sure if all decoders can report the profile > or level that they detect. Is that really a problem when the READ_ONLY flag is set? I thought it was designed to fit this specific case, when the driver reports a value that userspace cannot affect. Otherwise, I agree that having a bitmask type would be a better fit, but I think it would be beneficial to keep the already-defined control and associated values, which implies using the menu control type for both encoders and decoders. If this is not an option, I would be in favour of adding per-codec read- only bitmask controls (e.g. for H264 something like V4L2_CID_MPEG_VIDEO_H264_PROFILE_SUPPORT) that expose the already- existing profile/level definitions as bit identifiers (a bit like coda is using them to craft a mask for the menu items to blacklist) for decoding only. What do you think? Cheers, Paul --=20 Paul Kocialkowski, Bootlin (formerly Free Electrons) Embedded Linux and kernel engineering https://bootlin.com --=-+VTkoTexxFsbtNEWLvNM Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEJZpWjZeIetVBefti3cLmz3+fv9EFAltoESgACgkQ3cLmz3+f v9H4kQf+JjTLKrtEenbQpOEvhSMC+ifMl8LqKsEUpahWs9sfG3f9xx3sY/FsHF74 B8K+N5SkzVDhXNeoM9L8Tyc6XNiPHprOI9d7usUgP8uznf6FJU2U/FGoq1XjQeyh tOYnOcUj1rmoPGPHnC8dERVUI/NaB0NJhNpRUlW+S9pfdSbgKDcE+BTN5iIvdnx9 4jh4bcHQdF++Z7echWcJwDMeNh0TEb0PVFugtorgjDU4k7NBgTaHvFXsMKDfw4vA 71bmr2xl3kjplBBBa5CNR2a0w4lXK6oh6u5aHqRm9+KuqIsIkEU9l+EoyGkkGhyZ d+i0WuDayg3bx8kt3wbOWOqT9G9tGg== =6By3 -----END PGP SIGNATURE----- --=-+VTkoTexxFsbtNEWLvNM--