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Message-ID: <763308daa3304ef3cf011b4ca7b9c5c006627c90.camel@collabora.com>
Subject: Re: [PATCH v6 11/17] media: uapi: Add
 V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS control
From:   Nicolas Dufresne <nicolas.dufresne@collabora.com>
To:     Jernej =?UTF-8?Q?=C5=A0krabec?= <jernej.skrabec@gmail.com>,
        mchehab@kernel.org, ezequiel@vanguardiasur.com.ar,
        p.zabel@pengutronix.de, gregkh@linuxfoundation.org,
        mripard@kernel.org, paul.kocialkowski@bootlin.com, wens@csie.org,
        samuel@sholland.org, andrzej.p@collabora.com,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Benjamin Gaignard <benjamin.gaignard@collabora.com>
Cc:     linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-rockchip@lists.infradead.org, linux-staging@lists.linux.dev,
        linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev,
        kernel@collabora.com
Date:   Wed, 01 Jun 2022 13:07:54 -0400
In-Reply-To: <11988268.O9o76ZdvQC@jernej-laptop>
References: <20220527143134.3360174-1-benjamin.gaignard@collabora.com>
         <2102878.irdbgypaU6@kista>
         <95261aa18425e8f5571888a41ee03d9dfd2814b9.camel@collabora.com>
         <11988268.O9o76ZdvQC@jernej-laptop>
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Le mercredi 01 juin 2022 =C3=A0 18:35 +0200, Jernej =C5=A0krabec a =C3=A9cr=
it=C2=A0:
> > I believe its defined following "Table A.8 =E2=80=93 General tier and l=
evel limits".
> > With the assumption there will never be a level 7 (which I think is fai=
r).
> > If anyone saw other reasons for this limit, let me know.
> >=20
> > This is a worse case scenario, this is quite unlikely in practice, so w=
hile
> > performance might be a disaster if your craft a stream for that case, I
> > don't think it will ever happen in real life.
>=20
> But do we really need to cover worst case scenario? In theory, one driver=
 can=20
> set limit to (for example) max 100 slices and if there is a frame with 60=
0=20
> slices, userspace app would submit 6 decode requests. Basically the same =
way=20
> it's done today. While not as performant, it would be good compromise bet=
ween=20
> resources and speed.

The limit here is to prevent userland from tricking the kernel into doing v=
ery
big allocation. But with dynamic array, you'll allocate just the right amou=
nt.

Nicolas