From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.bootlin.com ([62.4.15.54]:45849 "EHLO mail.bootlin.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750752AbeCLI0J (ORCPT ); Mon, 12 Mar 2018 04:26:09 -0400 Message-ID: <1520843103.1513.8.camel@bootlin.com> Subject: Re: [RFCv4,19/21] media: vim2m: add request support From: Paul Kocialkowski To: Tomasz Figa , Dmitry Osipenko Cc: Alexandre Courbot , Mauro Carvalho Chehab , Hans Verkuil , Laurent Pinchart , Pawel Osciak , Marek Szyprowski , Sakari Ailus , Gustavo Padovan , Linux Media Mailing List , Linux Kernel Mailing List , Maxime Ripard Date: Mon, 12 Mar 2018 09:25:03 +0100 In-Reply-To: References: <20180220044425.169493-20-acourbot@chromium.org> <1520440654.1092.15.camel@bootlin.com> <6470b45d-e9dc-0a22-febc-cd18ae1092be@gmail.com> <1520842245.1513.5.camel@bootlin.com> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-vi8lL/WrEHkMCOMTypE+" Mime-Version: 1.0 Sender: linux-media-owner@vger.kernel.org List-ID: --=-vi8lL/WrEHkMCOMTypE+ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi, On Mon, 2018-03-12 at 17:15 +0900, Tomasz Figa wrote: > Hi Paul, Dmitry, >=20 > On Mon, Mar 12, 2018 at 5:10 PM, Paul Kocialkowski > wrote: > > Hi, > >=20 > > On Sun, 2018-03-11 at 22:42 +0300, Dmitry Osipenko wrote: > > > Hello, > > >=20 > > > On 07.03.2018 19:37, Paul Kocialkowski wrote: > > > > Hi, > > > >=20 > > > > First off, I'd like to take the occasion to say thank-you for > > > > your > > > > work. > > > > This is a major piece of plumbing that is required for me to add > > > > support > > > > for the Allwinner CedarX VPU hardware in upstream Linux. Other > > > > drivers, > > > > such as tegra-vde (that was recently merged in staging) are also > > > > badly > > > > in need of this API. > > >=20 > > > Certainly it would be good to have a common UAPI. Yet I haven't > > > got my > > > hands on > > > trying to implement the V4L interface for the tegra-vde driver, > > > but > > > I've taken a > > > look at Cedrus driver and for now I've one question: > > >=20 > > > Would it be possible (or maybe already is) to have a single IOCTL > > > that > > > takes input/output buffers with codec parameters, processes the > > > request(s) and returns to userspace when everything is done? > > > Having 5 > > > context switches for a single frame decode (like Cedrus VAAPI > > > driver > > > does) looks like a bit of overhead. > >=20 > > The V4L2 interface exposes ioctls for differents actions and I don't > > think there's a combined ioctl for this. The request API was > > introduced > > precisely because we need to have consistency between the various > > ioctls > > needed for each frame. Maybe one single (atomic) ioctl would have > > worked > > too, but that's apparently not how the V4L2 API was designed. > >=20 > > I don't think there is any particular overhead caused by having n > > ioctls > > instead of a single one. At least that would be very surprising > > IMHO. >=20 > Well, there is small syscall overhead, which normally shouldn't be > very painful, although with all the speculative execution hardening, > can't be sure of anything anymore. :) Oh, my mistake then, I had it in mind that it is not really something noticeable. Hopefully, it won't be a limiting factor in our cases. > Hans and Alex can correct me if I'm wrong, but I believe there is a > more atomic-like API being planned, which would only need one IOCTL to > do everything. However, that would be a more serious change to the > V4L2 interfaces, so should be decoupled from Request API itself. >=20 > Best regards, > Tomasz --=20 Paul Kocialkowski, Bootlin (formerly Free Electrons) Embedded Linux and kernel engineering https://bootlin.com --=-vi8lL/WrEHkMCOMTypE+ 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+fv9EFAlqmOV8ACgkQ3cLmz3+f v9Enqwf/dGlUworp9wGBWUKSVsM7pgf2yfj2RcdyhkJ9JyD8udtaVguCtr+V45Ie Ve87E+0rWw97rRBHkZwL50g18s56PwsdYzNIv8p6w203LQ224RFDqSalCBkSxPWR QWCLz5PVsrKPWUdFTrcdsRviTAdqcsTAfarZ6hBVukhc0Uh8+sKS243AxN+BuaKz 9INTOr4HfLnYh/vLJjQf6n7CfKOyp12mfnIavkk75p24teRpjae9UNBrsbQJQ5d4 W9ncC8VVWXOgY41+FdkSCcLAUvrD75tGkAGUjF7xz102Or0J5djWSvR/PUjIBuMt s2+bmRRjii+T8U3PtwRyI8+3UXUH1Q== =J1Z1 -----END PGP SIGNATURE----- --=-vi8lL/WrEHkMCOMTypE+--