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Date:   Wed, 25 Mar 2020 09:04:09 +0000
To:     Neil Armstrong <narmstrong@baylibre.com>
From:   Simon Ser <contact@emersion.fr>
Cc:     "daniel@ffwll.ch" <daniel@ffwll.ch>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "mjourdan@baylibre.com" <mjourdan@baylibre.com>,
        Kevin Hilman <khilman@baylibre.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-amlogic@lists.infradead.org" 
        <linux-amlogic@lists.infradead.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
Reply-To: Simon Ser <contact@emersion.fr>
Subject: Re: [PATCH v4 7/8] drm/fourcc: amlogic: Add modifier definitions for the Scatter layout
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In-Reply-To: <20200325085025.30631-8-narmstrong@baylibre.com>
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 <20200325085025.30631-8-narmstrong@baylibre.com>
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On Wednesday, March 25, 2020 9:50 AM, Neil Armstrong <narmstrong@baylibre.c=
om> wrote:

> Amlogic uses a proprietary lossless image compression protocol and format
> for their hardware video codec accelerators, either video decoders or
> video input encoders.
>
> This introduces the Scatter Memory layout, means the header contains IOMM=
U
> references to the compressed frames content to optimize memory access
> and layout.
>
> In this mode, only the header memory address is needed, thus the content
> memory organization is tied to the current producer execution and cannot
> be saved/dumped neither transferrable between Amlogic SoCs supporting thi=
s
> modifier.

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 blacklist
of modifiers that don't work this way.

Example of such user-space:
https://gitlab.freedesktop.org/mstoeckl/waypipe/