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Subject: Re: [PATCH v4 7/8] drm/fourcc: amlogic: Add modifier definitions for
 the Scatter layout
To:     Pekka Paalanen <ppaalanen@gmail.com>
Cc:     Simon Ser <contact@emersion.fr>,
        "mjourdan@baylibre.com" <mjourdan@baylibre.com>,
        Kevin Hilman <khilman@baylibre.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "linux-amlogic@lists.infradead.org" 
        <linux-amlogic@lists.infradead.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
References: <20200325085025.30631-1-narmstrong@baylibre.com>
 <20200325085025.30631-8-narmstrong@baylibre.com>
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 <b1386ef5-c3e3-c07b-5982-e3f02441b431@baylibre.com>
 <20200325154921.2a87930c@eldfell.localdomain>
From:   Neil Armstrong <narmstrong@baylibre.com>
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Organization: Baylibre
Message-ID: <a385e2f6-52fa-e195-15e0-2132befc9f35@baylibre.com>
Date:   Wed, 25 Mar 2020 17:18:15 +0100
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 protected-headers="v1"
From: Neil Armstrong <narmstrong@baylibre.com>
To: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Simon Ser <contact@emersion.fr>,
 "mjourdan@baylibre.com" <mjourdan@baylibre.com>,
 Kevin Hilman <khilman@baylibre.com>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
 "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
 "linux-amlogic@lists.infradead.org" <linux-amlogic@lists.infradead.org>,
 "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>
Message-ID: <a385e2f6-52fa-e195-15e0-2132befc9f35@baylibre.com>
Subject: Re: [PATCH v4 7/8] drm/fourcc: amlogic: Add modifier definitions for
 the Scatter layout
References: <20200325085025.30631-1-narmstrong@baylibre.com>
 <20200325085025.30631-8-narmstrong@baylibre.com>
 <JgBZ7eZYMgXRNu_-E4ItS1bud9mEe15xptZEX_XhsM_h8_iIZTOmPokEVxPJYwX0wP0pmb5p-ymubyyZP3kVbcfuDNdmM0__L8wBR5IykfE=@emersion.fr>
 <b1386ef5-c3e3-c07b-5982-e3f02441b431@baylibre.com>
 <20200325154921.2a87930c@eldfell.localdomain>
In-Reply-To: <20200325154921.2a87930c@eldfell.localdomain>

--xYRIM8FT5PkffJgu9IzYLanBQWKZrnDyH
Content-Type: text/plain; charset=windows-1252
Content-Language: en-US
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Hi,

On 25/03/2020 14:49, Pekka Paalanen wrote:
> On Wed, 25 Mar 2020 11:24:15 +0100
> Neil Armstrong <narmstrong@baylibre.com> wrote:
>=20
>> Hi,
>>
>> On 25/03/2020 10:04, Simon Ser wrote:
>>> On Wednesday, March 25, 2020 9:50 AM, Neil Armstrong <narmstrong@bayl=
ibre.com> wrote:
>>>  =20
>>>> Amlogic uses a proprietary lossless image compression protocol and f=
ormat
>>>> for their hardware video codec accelerators, either video decoders o=
r
>>>> video input encoders.
>>>>
>>>> This introduces the Scatter Memory layout, means the header contains=
 IOMMU
>>>> references to the compressed frames content to optimize memory acces=
s
>>>> and layout.
>>>>
>>>> In this mode, only the header memory address is needed, thus the con=
tent
>>>> memory organization is tied to the current producer execution and ca=
nnot
>>>> be saved/dumped neither transferrable between Amlogic SoCs supportin=
g this
>>>> modifier. =20
>>>
>>> I don't think this is suitable for modifiers. User-space relies on
>>> being able to copy a buffer from one machine to another over the
>>> network. It would be pretty annoying for user-space to have a blackli=
st
>>> of modifiers that don't work this way.
>>>
>>> Example of such user-space:
>>> https://gitlab.freedesktop.org/mstoeckl/waypipe/
>>>  =20
>>
>> I really understand your point, but this is one of the use-cases we ne=
ed solve.
>> This is why I split the fourcc patch and added an explicit comment.
>>
>> Please point me a way to display such buffer, the HW exists, works lik=
e that and
>> it's a fact and can't change.
>>
>> It will be the same for secure zero-copy buffers we can't map from use=
rspace, but
>> only the HW decoder can read/write and HW display can read.
>=20
> The comparison to secure buffers is a good one.
>=20
> Are buffers with the DRM_FORMAT_MOD_AMLOGIC_FBC_LAYOUT_SCATTER modifier=

> meaningfully mmappable to CPU always / sometimes / never /
> varies-and-cannot-know?

mmappable, yes in our WIP V4L2 driver in non-secure path, meaningful, abs=
olutely never.

So yeah, these should not be mmappable since not meaningful.

>=20
> Maybe this type should be handled similar to secure buffers, with the
> exception that they are not actually secured but only mostly
> inaccessible. Then again, I haven't looked at any of the secure buffer
> proposals.

Actually, the Amlogic platforms offers secure video path using these exac=
t
modifiers, AFAIK it doesn't support the NV12 dual-write output in secure.=


AFAIK last submission is from AMD, and it doesn't talk at all about mmapa=
bility
of the secure BOs.

Neil

>=20
>=20
> Thanks,
> pq
>=20


--xYRIM8FT5PkffJgu9IzYLanBQWKZrnDyH--

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