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

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Message-Id: <F8ED7EBD-FC71-4E40-98A0-DD239EF9371D@soulik.info>
Date:   Tue, 8 Jan 2019 15:40:08 +0800
From:   Ayaka <ayaka@...lik.info>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.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



Sent from my iPad

> On Jan 8, 2019, at 2:33 PM, Tomasz Figa <tfiga@...omium.org> wrote:
> 
>> On Mon, Jan 7, 2019 at 2:30 AM Ayaka <ayaka@...lik.info> wrote:
>> 
>> Hello Ezequiel
>> 
>> Sent from my iPad
>> 
>>>> On Jan 7, 2019, at 1:21 AM, Ezequiel Garcia <ezequiel@...guardiasur.com.ar> wrote:
>>>> 
>>>> 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?
>>> 
>> For rk3328, yes, you see I didn’t draw them in the same box.
>>> 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".
>> No, you can’t assume which one is in the combo group, it can be various. you see, in the rk3328, the vdpu is paired with an avs+ decoder. That is why I use a virtual device standing for scheduler.
> 
> First of all, thanks for all the input. Having more understanding of
> the hardware and shortcomings of the current V4L2 APIs is really
> important to let us further evolve the API and make sure that it works
> for further use cases.
I replied the problems of the v4l2 request API in the other threads. I am waiting the feedback from those threads.
> 
> As for the Device Tree itself, it doesn't always describe the hardware
> in 100%.
Also please note the merged device tree for the video codec won’t fix for most of the rockchip platform.
> Most of the time it's just the necessary information to
> choose and instantiate the right drivers and bind to the right
> hardware resources. The information on which hardware instances on the
> SoC can work independently can of course be described in DT (e.g. by
> sub-nodes of a video-codec complex OR a set of phandles, e.g.
> rockchip,shared-instances), but it's also perfectly fine to defer this
> kind of knowledge to the drivers themselves.
I wish there is a common mechanism for those device would share some resources. Although there is a multiple functions framework,  but that is not I want. They are multiple functions but they are used at the same time not separately.
> 
> Best regards,
> Tomasz