linux-kernel - Re: [PATCH 4/4] arm64: dts: rockchip: add video codec for rk3399

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Date:   Sun, 6 Jan 2019 14:21:37 -0300
From:   Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
To:     Ayaka <ayaka@...lik.info>
Cc:     Ezequiel Garcia <ezequiel@...labora.com>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        myy@...uyouyou.fr,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media <linux-media@...r.kernel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Heiko Stuebner <heiko@...ech.de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] arm64: dts: rockchip: add video codec for rk3399

On Sun, 6 Jan 2019 at 13:16, Ayaka <ayaka@...lik.info> wrote:
>
>
>
> Sent from my iPad
>
> > On Jan 7, 2019, at 12:04 AM, Ezequiel Garcia <ezequiel@...labora.com> wrote:
> >
> > On Sun, 2019-01-06 at 23:05 +0800, Ayaka wrote:
> >>> On Jan 6, 2019, at 10:22 PM, Ezequiel Garcia <ezequiel@...labora.com> wrote:
> >>>
> >>> Hi Randy,
> >>>
> >>> Thanks a lot for this patches. They are really useful
> >>> to provide more insight into the VPU hardware.
> >>>
> >>> This change will make the vpu encoder and vpu decoder
> >>> completely independent, can they really work in parallel?
> >> As I said it depends on the platform, but with this patch, the user space would think they can work at the same time.
> >
> >
> > I think there is some confusion.
> >
> > The devicetree is one thing: it is a hardware representation,
> > a way to describe the hardware, for the kernel/bootloader to
> > parse.
> >
> > The userspace view will depend on the driver implementation.
> >
> > The current devicetree and driver (without your patches),
> > model the VPU as a single piece of hardware, exposing a decoder
> > and an encoder.
> >
> > The V4L driver will then create two video devices, i.e. /dev/videoX
> > and /dev/videoY. So userspace sees an independent view of the
> > devices.
> >
> I knew that, the problem is that the driver should not always create a decoder and encoder pair, they may not exist at some platforms, even some platforms doesn’t have a encoder. You may have a look on the rk3328 I post on the first email as example.

That is correct. But that still doesn't tackle my question: is the
hardware able to run a decoding and an encoding job in parallel?

If not, then it's wrong to describe them as independent entities.

> > However, they are internally connected, and thus we can
> > easily avoid two jobs running in parallel.
> >
> That is what the mpp service did in my patches, handing the relationship between each devices. And it is not a easy work, maybe a 4k decoder would be blocked by another high frame rate encoding work or another decoder session. The vendor kernel have more worry about this,  but not in this version.

Right. That is one way to design it. Another way is having a single
devicetree node for the VPU encoder/decoder "complex".

Thanks for the input!
-- 
Ezequiel García, VanguardiaSur
www.vanguardiasur.com.ar